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Minimal annual rainfall in arid environments results in low productivity ecosystems with fluctuating food availability. Large mammalian predators that require frequent consumption of vertebrate prey tend to be less abundant in desert environments; however, such environments often support numerous large‐bodied carnivorous reptiles. Diet is a fundamental component of an animal’s ecology, and we explore the diets of three coexisting, sympatric Varanus species occurring in arid Australia: V. tristis, V. gouldii and V. panoptes. We hypothesized that the diet of varanids living in arid environments would primarily consist of relatively abundant invertebrate prey, and that vertebrate prey items would largely be limited to opportunistically consumed mammalian carrion and small reptilian species. All three Varanus species had high dietary overlap and broad, generalist diets. Invertebrate prey, particularly Orthoptera, were key to the diets of all three species. Vertebrate prey was infrequently consumed by all three Varanus species; however, when consumed, tended to comprise small reptilian species and mammalian carrion. Unlike large mammalian predators, varanids can survive on invertebrate prey and infrequent feeds and can aestivate when conditions become unfavourable, contributing to their success in arid environments.

Australian animals have suffered exceptionally high rates of extinction over the last 200 years, with the greatest impact seen in ‘critical weight range’ (CWR; 35g–5.5kg) terrestrial mammals. These declines are probably driven by introduced eutherian predators as CWR species fall within the preferred prey size of feral cats and red foxes. The predation impact of these introduced predators in Australia is more than double that of native predators, likely due to the lack of co‐evolution between predator and prey. Marsupials show marked diversity in how they move during escape (e.g., ‘outrun’ or ‘outmaneuver’), which could make some species more vulnerable to the hunting strategies of eutherian predators than others. This study investigates the effect of morphological variation between CWR species on their locomotor performance during escape. We present a comparative analysis of hind limb myology in nine species of CWR marsupials with representatives of quadrupedal and bipedal taxa. We predicted that differences in muscle morphology would be reflected in locomotor performance (i.e., speed, acceleration, agility). To quantify hind limb morphology, we measured muscle architectural properties including mass, fascicle length and physiological cross‐sectional areas (PCSA) of key muscles, as well as distribution of functional groups and differences in muscle attachments. We compared this muscle data to preliminary escape locomotion data collected from these same species. Differences in both hind limb morphology and escape locomotion between species were found, with species which showed a propensity for jinking (‘outmaneuver’) separating from species that fled in a straight line with a burst of speed (‘outrun’). This preliminary analysis gives us an integrated view of morphology and locomotor behavior to better understand the mechanistic basis of escape performance in CWR marsupials.

Minimal annual rainfall in arid environments results in low productivity ecosystems with fluctuating food availability. Large mammalian predators that require frequent consumption of vertebrate prey tend to be less abundant in desert environments; however, such environments often support numerous large‐bodied carnivorous reptiles. Diet is a fundamental component of an animal’s ecology, and we explore the diets of three coexisting, sympatric Varanus species occurring in arid Australia: V. tristis, V. gouldii and V. panoptes. We hypothesized that the diet of varanids living in arid environments would primarily consist of relatively abundant invertebrate prey, and that vertebrate prey items would largely be limited to opportunistically consumed mammalian carrion and small reptilian species. All three Varanus species had high dietary overlap and broad, generalist diets. Invertebrate prey, particularly Orthoptera, were key to the diets of all three species. Vertebrate prey was infrequently consumed by all three Varanus species; however, when consumed, tended to comprise small reptilian species and mammalian carrion. Unlike large mammalian predators, varanids can survive on invertebrate prey and infrequent feeds and can aestivate when conditions become unfavourable, contributing to their success in arid environments.

Australian animals have suffered exceptionally high rates of extinction over the last 200 years, with the greatest impact seen in ‘critical weight range’ (CWR; 35g–5.5kg) terrestrial mammals. These declines are probably driven by introduced eutherian predators as CWR species fall within the preferred prey size of feral cats and red foxes. The predation impact of these introduced predators in Australia is more than double that of native predators, likely due to the lack of co‐evolution between predator and prey. Marsupials show marked diversity in how they move during escape (e.g., ‘outrun’ or ‘outmaneuver’), which could make some species more vulnerable to the hunting strategies of eutherian predators than others. This study investigates the effect of morphological variation between CWR species on their locomotor performance during escape. We present a comparative analysis of hind limb myology in nine species of CWR marsupials with representatives of quadrupedal and bipedal taxa. We predicted that differences in muscle morphology would be reflected in locomotor performance (i.e., speed, acceleration, agility). To quantify hind limb morphology, we measured muscle architectural properties including mass, fascicle length and physiological cross‐sectional areas (PCSA) of key muscles, as well as distribution of functional groups and differences in muscle attachments. We compared this muscle data to preliminary escape locomotion data collected from these same species. Differences in both hind limb morphology and escape locomotion between species were found, with species which showed a propensity for jinking (‘outmaneuver’) separating from species that fled in a straight line with a burst of speed (‘outrun’). This preliminary analysis gives us an integrated view of morphology and locomotor behavior to better understand the mechanistic basis of escape performance in CWR marsupials.

We review the use of clay models to explore questions about predation rates on small vertebrate taxa that are typically difficult to observe directly. The use of models has a relatively long history and we examine the range of taxa studied, which includes squamate reptiles, amphibians, mammals and birds. Within this review, we have also included studies of model eggs, which are used in nest predation studies. We review the questions that have been asked and the interpretations arising from the data. The use of clay model animals has provided us with insights into how differences in prey morphology, size, and colour influence the rate at which they are attacked by predators. This allows us insights into the ecological, behavioural and evolutionary selective pressures of different predators on small vertebrate prey, including analysis of what characteristics predators target and how predators approach their prey (e.g. which part of the body is attacked). Further available interpretations include how regional and habitat variation influences predation events on models. We also briefly discuss the potential for clay models to study interspecific sociality and competition. Finally, we review the problems and limitations with the method and make some suggestions for further studies and amendments to help standardize this creative tool for ecological research.

Bite force is often used as a predictive indicator of an animal's feeding ecology, although the premise that there is a direct link between diet and cranial morphology can be difficult to test empirically. Studies that have examined this question tend to rely on generalizations of a species' diet, and age and sex differences are rarely considered. Red foxes (Vulpes vulpes) are introduced predators in Australia, allowing large sample size collection through culling for comparison of skull morphology (size, morphometry, weight), demographics (age, sex) and diet (stomach contents). Over half (57%) of the 540 animals we sampled were juveniles (<1 year old; dispersing from their natal sites) and most variation in skull morphometry was driven by age; adults had significantly more robust skulls than juveniles, with greater estimated bite force. Sexual dimorphism (body mass and body length) was reflected in longer, heavier skulls of males. We also recorded significant sex and age differences in diet. Sheep carrion comprised 47-65% of diet volume; however, adult females ate less sheep but had more mice and invertebrates in their diet than males or juveniles of both sexes. This dietary separation for adult females does not appear to be directly due to estimated bite force constraints, but probably rather prey availability, which may reflect feeding behaviour and space use patterns. Juveniles (both sexes) showed as much consumption of sheep carrion as adult males, despite their lower estimated bite force than adults. This is the first study that directly compares ontogenetic and sex differences in the diet of a carnivore together with their cranial morphology and estimated bite force, and highlights limitations of inferring diet partitioning from skull morphology alone

Islands play an important conservation role due to high rates of speciation as well as providing a predator-free refuge environment for species that are vulnerable to terrestrial predation on the mainland. Many animals show marked 'island tameness' on predator-free islands, reducing costly escape responses in the absence of predation threat. Island tameness also translates to altered responses toward humans, making many island species attractive for wildlife tourism. We explored temporal and spatial differences in behavioral responses in the Rottnest Island quokka Setonix brachyurus. This marsupial is an excellent species to test for the effects of ecotourism, as well as of being conservation significance (IUCN-listed as vulnerable). Comparing escape responses for n = 339 individuals in high tourism and low tourism seasons, quokkas at tourism sites allowed a person to approach closer before moving away compared with non-tourisms sites, and two-thirds of individuals around tourism sites allowed a person to approach within 1 m (compared with 14% of individuals at non-tourism sites). For n = 67 ad hoc interactions with tourists, quokkas would only move away from an interaction with a tourist when the tourist group was noisy or there was an attempt to touch the animal. Time budgets (n = 379 individuals) showed that quokkas spent more time in group behavior and locomotion, but less in vigilance and feeding for tourism sites compared with non-tourism sites. Understanding the impact of ecotourism on animal behavior will help to frame conservation management actions to ensure persistence of threatened wildlife species. We propose two models describing animal responses toward ecotourism: spatial separation according to animal temperament or temporal adjustment due to learned habituation. These models are not mutually exclusive and we suggest that both spatial separation and habitation are likely evident for Rottnest quokkas. We discuss the implications of these results for p

We review the use of clay models to explore questions about predation rates on small vertebrate taxa that are typically difficult to observe directly. The use of models has a relatively long history and we examine the range of taxa studied, which includes squamate reptiles, amphibians, mammals and birds. Within this review, we have also included studies of model eggs, which are used in nest predation studies. We review the questions that have been asked and the interpretations arising from the data. The use of clay model animals has provided us with insights into how differences in prey morphology, size, and colour influence the rate at which they are attacked by predators. This allows us insights into the ecological, behavioural and evolutionary selective pressures of different predators on small vertebrate prey, including analysis of what characteristics predators target and how predators approach their prey (e.g. which part of the body is attacked). Further available interpretations include how regional and habitat variation influences predation events on models. We also briefly discuss the potential for clay models to study interspecific sociality and competition. Finally, we review the problems and limitations with the method and make some suggestions for further studies and amendments to help standardize this creative tool for ecological research.

Bite force is often used as a predictive indicator of an animal's feeding ecology, although the premise that there is a direct link between diet and cranial morphology can be difficult to test empirically. Studies that have examined this question tend to rely on generalizations of a species' diet, and age and sex differences are rarely considered. Red foxes (Vulpes vulpes) are introduced predators in Australia, allowing large sample size collection through culling for comparison of skull morphology (size, morphometry, weight), demographics (age, sex) and diet (stomach contents). Over half (57%) of the 540 animals we sampled were juveniles (<1 year old; dispersing from their natal sites) and most variation in skull morphometry was driven by age; adults had significantly more robust skulls than juveniles, with greater estimated bite force. Sexual dimorphism (body mass and body length) was reflected in longer, heavier skulls of males. We also recorded significant sex and age differences in diet. Sheep carrion comprised 47-65% of diet volume; however, adult females ate less sheep but had more mice and invertebrates in their diet than males or juveniles of both sexes. This dietary separation for adult females does not appear to be directly due to estimated bite force constraints, but probably rather prey availability, which may reflect feeding behaviour and space use patterns. Juveniles (both sexes) showed as much consumption of sheep carrion as adult males, despite their lower estimated bite force than adults. This is the first study that directly compares ontogenetic and sex differences in the diet of a carnivore together with their cranial morphology and estimated bite force, and highlights limitations of inferring diet partitioning from skull morphology alone

Islands play an important conservation role due to high rates of speciation as well as providing a predator-free refuge environment for species that are vulnerable to terrestrial predation on the mainland. Many animals show marked 'island tameness' on predator-free islands, reducing costly escape responses in the absence of predation threat. Island tameness also translates to altered responses toward humans, making many island species attractive for wildlife tourism. We explored temporal and spatial differences in behavioral responses in the Rottnest Island quokka Setonix brachyurus. This marsupial is an excellent species to test for the effects of ecotourism, as well as of being conservation significance (IUCN-listed as vulnerable). Comparing escape responses for n = 339 individuals in high tourism and low tourism seasons, quokkas at tourism sites allowed a person to approach closer before moving away compared with non-tourisms sites, and two-thirds of individuals around tourism sites allowed a person to approach within 1 m (compared with 14% of individuals at non-tourism sites). For n = 67 ad hoc interactions with tourists, quokkas would only move away from an interaction with a tourist when the tourist group was noisy or there was an attempt to touch the animal. Time budgets (n = 379 individuals) showed that quokkas spent more time in group behavior and locomotion, but less in vigilance and feeding for tourism sites compared with non-tourism sites. Understanding the impact of ecotourism on animal behavior will help to frame conservation management actions to ensure persistence of threatened wildlife species. We propose two models describing animal responses toward ecotourism: spatial separation according to animal temperament or temporal adjustment due to learned habituation. These models are not mutually exclusive and we suggest that both spatial separation and habitation are likely evident for Rottnest quokkas. We discuss the implications of these results for p

The escape behaviour of organisms that retreat to shelter to avoid predators is influenced by availability and quality (e.g. appropriate size) of shelters. We examined escape behaviour (flight initiation distance, distance fled to shelter) of the crab Leptograpsus variegatus, relative to shelter size and distribution on a shoreline with multiple shelters and on a shoreline with limited shelter. Larger crabs tended to be nearer to larger shelters than smaller crabs and fled sooner and further than smaller crabs. Larger crabs often fled past the nearest shelters if they were too small. Group size increased at the site with fewer shelters, but this did not influence flight behaviour. We conclude that the availability of shelters and body size influences escape behaviour of these crabs.

The escape behaviour of organisms that retreat to shelter to avoid predators is influenced by availability and quality (e.g. appropriate size) of shelters. We examined escape behaviour (flight initiation distance, distance fled to shelter) of the crab Leptograpsus variegatus, relative to shelter size and distribution on a shoreline with multiple shelters and on a shoreline with limited shelter. Larger crabs tended to be nearer to larger shelters than smaller crabs and fled sooner and further than smaller crabs. Larger crabs often fled past the nearest shelters if they were too small. Group size increased at the site with fewer shelters, but this did not influence flight behaviour. We conclude that the availability of shelters and body size influences escape behaviour of these crabs.

Optimal escape theory predicts that animals should moderate their flight responses according to the level of risk represented by a potential predator. This theory should apply even when organisms are habituated to disturbance, and how animals respond to human presence is likely to determine their success exploiting urban habitats. Therefore, urban animals should be sensitive to cues that inform them about levels of risk, allowing them to reduce costs by not overreacting to innocuous stimuli, while ensuring that they are nevertheless reactive to genuinely threatening stimuli. We tested this at a highly urbanized site in New York City, where eastern grey squirrels appear to pay little attention to humans. Squirrels were approached tangentially on a trajectory that took the observer within ∼2m of them and we measured alert distance, flight initiation distance (FID), and distance fled for each focal individual. Squirrels showed little sign of being alerted to the pedestrian if he remained on the footpath and did not look at them (only 5% of individuals moved away), but 90% of squirrels moved away, with longer FID and flight distance, when approached by a pedestrian that moved off the footpaths and looked at them. Squirrels therefore modulate their reactions when pedestrians behave in a predictable manner (i.e. remaining on the footpaths) and are also sensitive to the direction of attention of humans, reducing unnecessary responses, and are thereby likely to be increasing their ability to persist in this urban environment. Previous studies have emphasized the behavioural plasticity of successful urban wildlife species. In this study, we emphasize the importance of disturbance monitoring by successful urban exploiters, allowing them to vary their behavioural responses according to the level of risk to which they are exposed.

Optimal escape theory predicts that animals should moderate their flight responses according to the level of risk represented by a potential predator. This theory should apply even when organisms are habituated to disturbance, and how animals respond to human presence is likely to determine their success exploiting urban habitats. Therefore, urban animals should be sensitive to cues that inform them about levels of risk, allowing them to reduce costs by not overreacting to innocuous stimuli, while ensuring that they are nevertheless reactive to genuinely threatening stimuli. We tested this at a highly urbanized site in New York City, where eastern grey squirrels appear to pay little attention to humans. Squirrels were approached tangentially on a trajectory that took the observer within ∼2m of them and we measured alert distance, flight initiation distance (FID), and distance fled for each focal individual. Squirrels showed little sign of being alerted to the pedestrian if he remained on the footpath and did not look at them (only 5% of individuals moved away), but 90% of squirrels moved away, with longer FID and flight distance, when approached by a pedestrian that moved off the footpaths and looked at them. Squirrels therefore modulate their reactions when pedestrians behave in a predictable manner (i.e. remaining on the footpaths) and are also sensitive to the direction of attention of humans, reducing unnecessary responses, and are thereby likely to be increasing their ability to persist in this urban environment. Previous studies have emphasized the behavioural plasticity of successful urban wildlife species. In this study, we emphasize the importance of disturbance monitoring by successful urban exploiters, allowing them to vary their behavioural responses according to the level of risk to which they are exposed.

Little is known about how season influences burrowing activity, burrow structure or reproductive behaviour in subterranean mammals. We excavated burrow systems of male and female Georychus capensis, a solitary, subterranean rodent, in winter (wet season) and summer (dry season) to investigate whether, if any, seasonal differences were due to putative mate-seeking behaviour of males. Burrow structure differed between seasons but not between sexes. For both sexes, summer burrows were shorter and covered a smaller area, but explored the surrounding environment more efficiently than winter burrows. Summer burrows had fewer mounds, which indicated that less expansion of the burrow systems occurred during this season. We discuss these differences in exploration and the use of the environment between seasons in terms of mating strategies of G.capensis and observed levels of sexual dimorphism in our populations. This study supports recent ideas regarding sexual selection relating to exaggerated traits in females, which affect a female's ability to acquire reproductive resources that often appear similar to that selected for by males.

Cities may represent one of the most challenging environments for carnivorous mammals. For example, cities have a dearth of vegetation and other natural resources, coupled with increased habitat fragmentation and an abundance of roads as well as altered climate (e.g. temperature, light, rainfall and water runoff). It is therefore intriguing that several carnivore species have become established in cities across the globe. Medium-sized carnivores such as the red fox, coyote, Eurasian badger and raccoon not only survive in cities but also have managed to exploit anthropogenic food sources and shelter to their significant advantage, achieving higher population densities than are found under natural conditions. In addition, although they may not live permanently within cities, even large carnivores such as bears, wolves and hyaenas derive significant benefit from living adjacent to urbanized areas. In this review, we examine the history of urban adaptation by mammalian carnivores, explore where they are living, what they eat, what kills them and the behavioural consequences of living in urban areas. We review the biology of urban carnivores, exploring traits such as body size and dietary flexibility. Finally, we consider the consequences of having populations of carnivores in urbanized areas, both for humans and for these charismatic mammals. In conclusion, in a time of massive environmental change across the globe, the continuing encroachment of urbanization upon wilderness areas is substantially reducing the availability of natural habitats for many species; therefore, understanding the biology of any taxon that is able to adapt to and exploit anthropogenically disturbed systems must aid us in both controlling and developing suitable conservation measures for the future of such species.

Little is known about how season influences burrowing activity, burrow structure or reproductive behaviour in subterranean mammals. We excavated burrow systems of male and female Georychus capensis, a solitary, subterranean rodent, in winter (wet season) and summer (dry season) to investigate whether, if any, seasonal differences were due to putative mate-seeking behaviour of males. Burrow structure differed between seasons but not between sexes. For both sexes, summer burrows were shorter and covered a smaller area, but explored the surrounding environment more efficiently than winter burrows. Summer burrows had fewer mounds, which indicated that less expansion of the burrow systems occurred during this season. We discuss these differences in exploration and the use of the environment between seasons in terms of mating strategies of G.capensis and observed levels of sexual dimorphism in our populations. This study supports recent ideas regarding sexual selection relating to exaggerated traits in females, which affect a female's ability to acquire reproductive resources that often appear similar to that selected for by males.

Cities may represent one of the most challenging environments for carnivorous mammals. For example, cities have a dearth of vegetation and other natural resources, coupled with increased habitat fragmentation and an abundance of roads as well as altered climate (e.g. temperature, light, rainfall and water runoff). It is therefore intriguing that several carnivore species have become established in cities across the globe. Medium-sized carnivores such as the red fox, coyote, Eurasian badger and raccoon not only survive in cities but also have managed to exploit anthropogenic food sources and shelter to their significant advantage, achieving higher population densities than are found under natural conditions. In addition, although they may not live permanently within cities, even large carnivores such as bears, wolves and hyaenas derive significant benefit from living adjacent to urbanized areas. In this review, we examine the history of urban adaptation by mammalian carnivores, explore where they are living, what they eat, what kills them and the behavioural consequences of living in urban areas. We review the biology of urban carnivores, exploring traits such as body size and dietary flexibility. Finally, we consider the consequences of having populations of carnivores in urbanized areas, both for humans and for these charismatic mammals. In conclusion, in a time of massive environmental change across the globe, the continuing encroachment of urbanization upon wilderness areas is substantially reducing the availability of natural habitats for many species; therefore, understanding the biology of any taxon that is able to adapt to and exploit anthropogenically disturbed systems must aid us in both controlling and developing suitable conservation measures for the future of such species.

Animals may update their assessment of predation risk according to how a potential predator approaches them. For example, the predator's head and gaze orientation (direction of attention) may reveal its intentions, and faster-approaching predators are likely to represent greater risk. We examined the reactions of hadeda ibises Bostrychia hagedash. These large birds demonstrate a wide repertoire of responses to being approached (e.g. continuing to forage, slow walking, rapid escape walking, flight and alarm calling). Birds were approached tangentially 112 times by a human who either had the head and eyes directed towards (65 approaches) or directed away from (47 approaches) the birds to test the hypothesis that the direction of the observer's attention informs alert distance (AD) and flight initiation distance (FID) in these birds. Direction of attention had a significant effect on AD and FID as well as the likelihood of taking flight and alarm calling by hadedas, with birds appearing to associate attention directed towards them as an indication of increased risk. Hadedas were able to differentiate between the direction of attention of an approaching human, whether or not there were multiple other humans in the near vicinity. We also examined whether the observer's approach speed altered the birds' responses. Approach speed affected the birds' FID, suggesting that they perceive greater danger in a faster-approaching intruder compared with a slower-walking one. These results support the predictions of optimal escape theory and emphasize the high resolution of anti-predatory awareness in these birds. The marked success of hadeda ibises in urban environments may be due to their ability to become habituated to human presence and to modify their antipredator behaviour in response to subtle cues. These may be common traits of bird species that successfully adapt to urban environments.

Animals may update their assessment of predation risk according to how a potential predator approaches them. For example, the predator's head and gaze orientation (direction of attention) may reveal its intentions, and faster-approaching predators are likely to represent greater risk. We examined the reactions of hadeda ibises Bostrychia hagedash. These large birds demonstrate a wide repertoire of responses to being approached (e.g. continuing to forage, slow walking, rapid escape walking, flight and alarm calling). Birds were approached tangentially 112 times by a human who either had the head and eyes directed towards (65 approaches) or directed away from (47 approaches) the birds to test the hypothesis that the direction of the observer's attention informs alert distance (AD) and flight initiation distance (FID) in these birds. Direction of attention had a significant effect on AD and FID as well as the likelihood of taking flight and alarm calling by hadedas, with birds appearing to associate attention directed towards them as an indication of increased risk. Hadedas were able to differentiate between the direction of attention of an approaching human, whether or not there were multiple other humans in the near vicinity. We also examined whether the observer's approach speed altered the birds' responses. Approach speed affected the birds' FID, suggesting that they perceive greater danger in a faster-approaching intruder compared with a slower-walking one. These results support the predictions of optimal escape theory and emphasize the high resolution of anti-predatory awareness in these birds. The marked success of hadeda ibises in urban environments may be due to their ability to become habituated to human presence and to modify their antipredator behaviour in response to subtle cues. These may be common traits of bird species that successfully adapt to urban environments.

Damaraland mole-rats Fukomys damarensis are eusocial subterranean rodents that exhibit an extreme reproductive skew with one female and one or two males breeding. The non-reproductive individuals in the colony are reproductively suppressed, and yet show a rapid initiation of copulatory behaviour (within 1 h) when taken out of the colony and exposed to non-kin. Little is known about how these individuals can quickly become sexually active if the causes of suppression are removed. This study investigated circulating gonadotrophin concentrations [follicle stimulating hormone (FSH)] and testicular morphology and function in reproductive and non-reproductive male Damaraland mole-rats taken directly from their natal colonies and non-reproductive males that had been introduced to non-kin females outside their colony for 10 or 60 min. The main findings were that 60-min exposure males had a significantly heavier body mass-corrected testicular mass than reproductive males. In addition, the external seminiferous tubule diameter was significantly larger in reproductive males than in non-reproductive males, and the tubule lumen area was significantly greater in reproductive, 10 and 60-min exposure males than in non-reproductive males. Plasma concentrations of FSH were not different between the groups; however, the reproductive status significantly affected the area of testicular tissue stained immunopositive for the FSH receptor (FSH-R). Reproductive males had almost six times more FSH-R compared with non-reproductive males, and 60-min exposure males had eight times more FSH-R compared with non-reproductive males. In conclusion, the increase in the seminiferous tubular lumen area and the testicular FSH receptor content when non-reproductive male mole-rats come into contact with non-kin females indicates a rapid activation of testicular spermatogenic pathways to accompany the onset of copulatory behaviour, and is likely to be adaptive in allowing pairs formed of dispersing indivi

Damaraland mole-rats Fukomys damarensis are eusocial subterranean rodents that exhibit an extreme reproductive skew with one female and one or two males breeding. The non-reproductive individuals in the colony are reproductively suppressed, and yet show a rapid initiation of copulatory behaviour (within 1 h) when taken out of the colony and exposed to non-kin. Little is known about how these individuals can quickly become sexually active if the causes of suppression are removed. This study investigated circulating gonadotrophin concentrations [follicle stimulating hormone (FSH)] and testicular morphology and function in reproductive and non-reproductive male Damaraland mole-rats taken directly from their natal colonies and non-reproductive males that had been introduced to non-kin females outside their colony for 10 or 60 min. The main findings were that 60-min exposure males had a significantly heavier body mass-corrected testicular mass than reproductive males. In addition, the external seminiferous tubule diameter was significantly larger in reproductive males than in non-reproductive males, and the tubule lumen area was significantly greater in reproductive, 10 and 60-min exposure males than in non-reproductive males. Plasma concentrations of FSH were not different between the groups; however, the reproductive status significantly affected the area of testicular tissue stained immunopositive for the FSH receptor (FSH-R). Reproductive males had almost six times more FSH-R compared with non-reproductive males, and 60-min exposure males had eight times more FSH-R compared with non-reproductive males. In conclusion, the increase in the seminiferous tubular lumen area and the testicular FSH receptor content when non-reproductive male mole-rats come into contact with non-kin females indicates a rapid activation of testicular spermatogenic pathways to accompany the onset of copulatory behaviour, and is likely to be adaptive in allowing pairs formed of dispersing indivi

Caudal autotomy, the ability to shed the tail, is common in lizards as a response to attempted predation. Since Arnold's substantial review of caudal autotomy as a defence in reptiles 20 years ago, our understanding of the costs associated with tail loss has increased dramatically. In this paper, we review the incidence of caudal autotomy among lizards (Reptilia Sauria) with particular reference to questions posed by Arnold. We examine tail break frequencies and factors that determine occurrence of autotomy in natural populations (including anatomical mechanisms, predation efficiency and intensity, microhabitat preference, sex and ontogenetic differences, as well as intraspecific aggression). We also summarize the costs associated with tail loss in terms of survivorship and reproduction, focusing on potential mechanisms that influence fitness (i.e. locomotion costs, behavioural responses and metabolic costs). Finally, we examine the factors that may influence the facility with which autotomy takes place, including regeneration rate, body form and adaptive behaviour. Taking Arnold's example, we conclude with proposals for future research.

Armoured ground crickets Acanthoplus discoidalis (Bradyporidae) have an arsenal of defence mechanisms in response to attack. Males but not females can stridulate when attacked, while both sexes will bite and regurgitate upon provocation. They will also autohaemorrhage. Here we have quantified these responses, examining how individuals of both sexes respond to repeated simulated predatory attack from the side (grabbing the legs with forceps) or from above (grabbing the animal by the pronotum). We found different responses depending on the method of attack. When attack was directed from the side (at the legs) the crickets can bite their attacker and males stridulate intensely. About 62% of such attacks elicited an autohaemorrhage response, where the crickets squirt 13±22 mg of acrid-smelling haemolymph 43±63 mm from seams in the connective tissue between the trochanter and coxa of each leg and from under the pronotum. By contrast, animals attacked from above could not turn and bite their attacker, and stridulation was also reduced in males. About 86% of such attacks elicited an autohaemorrhage response with 19±19 mg of haemolymph projecting 10±30 mm from the body. Autohaemorrhaging is an effective form of chemical defence against bearded dragon lizards Pogona vitticeps (Agamidae) and Aca. discoidalis haemolymph applied to Gryllus bimaculatus nymphs (which have no such chemical defence) successfully saved them from predation by striped skinks Trachylepis punctatissima (Scincidae).

Caudal autotomy, the ability to shed the tail, is common in lizards as a response to attempted predation. Since Arnold's substantial review of caudal autotomy as a defence in reptiles 20 years ago, our understanding of the costs associated with tail loss has increased dramatically. In this paper, we review the incidence of caudal autotomy among lizards (Reptilia Sauria) with particular reference to questions posed by Arnold. We examine tail break frequencies and factors that determine occurrence of autotomy in natural populations (including anatomical mechanisms, predation efficiency and intensity, microhabitat preference, sex and ontogenetic differences, as well as intraspecific aggression). We also summarize the costs associated with tail loss in terms of survivorship and reproduction, focusing on potential mechanisms that influence fitness (i.e. locomotion costs, behavioural responses and metabolic costs). Finally, we examine the factors that may influence the facility with which autotomy takes place, including regeneration rate, body form and adaptive behaviour. Taking Arnold's example, we conclude with proposals for future research.

Armoured ground crickets Acanthoplus discoidalis (Bradyporidae) have an arsenal of defence mechanisms in response to attack. Males but not females can stridulate when attacked, while both sexes will bite and regurgitate upon provocation. They will also autohaemorrhage. Here we have quantified these responses, examining how individuals of both sexes respond to repeated simulated predatory attack from the side (grabbing the legs with forceps) or from above (grabbing the animal by the pronotum). We found different responses depending on the method of attack. When attack was directed from the side (at the legs) the crickets can bite their attacker and males stridulate intensely. About 62% of such attacks elicited an autohaemorrhage response, where the crickets squirt 13±22 mg of acrid-smelling haemolymph 43±63 mm from seams in the connective tissue between the trochanter and coxa of each leg and from under the pronotum. By contrast, animals attacked from above could not turn and bite their attacker, and stridulation was also reduced in males. About 86% of such attacks elicited an autohaemorrhage response with 19±19 mg of haemolymph projecting 10±30 mm from the body. Autohaemorrhaging is an effective form of chemical defence against bearded dragon lizards Pogona vitticeps (Agamidae) and Aca. discoidalis haemolymph applied to Gryllus bimaculatus nymphs (which have no such chemical defence) successfully saved them from predation by striped skinks Trachylepis punctatissima (Scincidae).

Autotomy is defined herein as the shedding of a body part, where (1) the loss of the body part is defensive (autotomy helps prevent the whole animal from being compromised and is in response to external stimuli); (2) shearing occurs by an intrinsic mechanism along a breakage plane (there has been selection for certain body parts to be pulled off easily); and (3) the loss is controlled - the animal moves away from the trapped limb, the loss is under some form of central control (neural or hormonal), or the body part is detached quickly. Autotomy (under this defensive definition) has evolved independently for a diverse array of body parts in many taxa; we have summarised available information for over 200 invertebrate species. The advantages of autotomy include escape from entrapment, an effective form of attack, expulsion of an infected body part or in limiting wounding. We discuss how the incidence of autotomy may therefore be correlated with various traits such as limb function, sex differences, other defence mechanisms, habitat disturbance, and sociality. There are also costs associated with autotomy. Short-term costs include loss of a specialised appendage or organ, reduced speed and stability, or even death. Long-term costs include compromised foraging and feeding (often leading to reduced growth), altered anti-predator, competitive or reproductive behaviour, and even defective development. Regenerating lost appendages may also incur significant costs for the individual. We examine the costs and benefits of autotomy, and discuss the evolutionary selective pressures that contribute to the prevalence and effectiveness of autotomy in invertebrates.

Autotomy is defined herein as the shedding of a body part, where (1) the loss of the body part is defensive (autotomy helps prevent the whole animal from being compromised and is in response to external stimuli); (2) shearing occurs by an intrinsic mechanism along a breakage plane (there has been selection for certain body parts to be pulled off easily); and (3) the loss is controlled - the animal moves away from the trapped limb, the loss is under some form of central control (neural or hormonal), or the body part is detached quickly. Autotomy (under this defensive definition) has evolved independently for a diverse array of body parts in many taxa; we have summarised available information for over 200 invertebrate species. The advantages of autotomy include escape from entrapment, an effective form of attack, expulsion of an infected body part or in limiting wounding. We discuss how the incidence of autotomy may therefore be correlated with various traits such as limb function, sex differences, other defence mechanisms, habitat disturbance, and sociality. There are also costs associated with autotomy. Short-term costs include loss of a specialised appendage or organ, reduced speed and stability, or even death. Long-term costs include compromised foraging and feeding (often leading to reduced growth), altered anti-predator, competitive or reproductive behaviour, and even defective development. Regenerating lost appendages may also incur significant costs for the individual. We examine the costs and benefits of autotomy, and discuss the evolutionary selective pressures that contribute to the prevalence and effectiveness of autotomy in invertebrates.