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Despite the important roles of assortative mating for understanding evolutionary processes, our knowledge on the variation in assortative mating across populations and breeding periods has been overshadowed by the greater attention given to general patterns. Obtaining data on mating pairs are difficult for most species; therefore, researchers often group data from different populations or breeding periods, which can increase positive biases in detecting and estimating assortative mating. We used a meta-analytic approach to investigate the biases caused by spatially or temporally pooling data and the assortative mating consistency across populations and breeding periods. We describe assortative mating patterns across and within animal taxa. We performed a systematic review to search studies reporting measures of size-assortative mating (SAM). Grouping data from multiple populations and seasons incurred positive biases. Overall, assortative mating moderately exhibited low repeatability in space and time, but it was inconsistent for most taxa. After excluding pooled measures, the average estimate for assortative mating was moderate and positive. Thus, our findings demonstrate that pooling data can produce misleading results. We also highlight the importance of further investigation of hypotheses that explain spatial and temporal variation in assortative mating, after its detection. Our study reinforces the significance of investigating mating patterns at various spatial and temporal scales before drawing broad conclusions.

The evolution of exclusive paternal care in arthropods is influenced by both natural and sexual selection. Male care may simultaneously increase egg protection against natural enemies and male attractiveness to ovipositing females. When caring males desert or die, their clutches may be adopted either by females that provide flexible compensation of parental care or by males that may increase their own attractiveness caring for unrelated eggs. Whether foster parents are as efficient as the original owner males in protecting the clutch is a question that has rarely been addressed. Here we experimentally evaluated the efficiency of egg attendance provided by males of the mud-nest harvestman Quindina limbata. We also tested whether unattended nests are adopted by females and/or unrelated males, and compared the efficiency of the protection provided by foster parents with that provided by the original owner males. We found that when males were present inside the nest, nest visits by egg predators were much lower than in experimentally unattended nests. Ten conspecifics (8 males, 2 females) adopted experimentally unattended nests. Foster males were as efficient as the original owner males in decreasing nest visits by egg predators. The most important conclusions of our study are: (1) male protection is crucial for egg survival because unattended nests are promptly attacked by predators; (2) flexible compensation of parental care by females is rare; (3) males adopt unrelated nests and protect the eggs as efficiently as original owner males, probably because egg attendance is a sexually selected behaviour.

Flexible compensatory parental care takes place when one parent increases its parental effort in response to its mate's reduction or absence. Although this behavioural response is well known in species with biparental care, the few cases attributed to species with uniparental care are usually based on descriptive observations of apparent compensation without a proper examination of its effects on offspring fitness. In the harvestman Serracutisoma proximum, a species with female uniparental care, harem-owning males stand on unattended clutches when the egg-tending females desert or die. Here, we experimentally investigated under field conditions whether this behaviour constitutes an example of true parental compensation. We evaluated the effects of ecological and life history factors on males' proximity to unattended clutches. We also presented egg predators to the harem-owning males and parental females when they were standing on their clutches and compared their aggressive responses. Finally, we compared egg survival between three manipulation groups: in the absence of both adults; in the presence of only the harem-owning males; and in the presence of the parental females. We observed that males spent considerably less time standing on clutches than parental females, rarely attacked potential egg predators (in contrast to parental females which commonly exhibited aggressive behaviours) and, ultimately, had no effect on offspring survival. Our results do not support the existence of paternal compensation in S. proximum. Instead, we hypothesize that males' behaviour comprises a tactic that increases: (1) fertilization success of unfertilized eggs retained by egg-tending females that temporarily abandon the clutch; and/or (2) mating success with newcomer mates that trade copulations for the opportunity to cannibalize the unattended offspring. This study demonstrates that it is imperative to formally test adaptive assumptions before deriving conclusions on the evolution of complex traits and their implications, as an apparently adaptive behaviour is not always what it seems.

Egg attendance imposes costs on parents, including decreased food intake and increased mortality risks. By concentrating parental activities when egg predation is greater and abiotic conditions are less stressful, parents may decrease these costs. Here, we quantify the costs and benefits of temporary egg desertion in the frog Thoropa taophora, whose males care for eggs on rocky shores. We tested hypotheses on the effect of the period of the day (day vs. night) and breeding site (exposed vs. protected from sunlight) on the frequency of temporary desertion, water loss, and egg predation. Using naturalistic observations, we show that parental males deserted their clutches more often during daytime and in exposed sites. Using a field experiment with agar models simulating adult males, we show that water loss was greater during daytime and in exposed sites. Finally, using field observations and a male removal experiment, we show that male presence improves egg survival and that egg predation was higher during the night, with no effect of breeding site. Because the main egg predators are conspecifics, which are mostly inactive when parental males are not attending their clutches, the costs of temporary desertion in terms of egg loss are relatively low when compared with the benefits related to decreased exposure of parental males to stressful abiotic conditions. In conclusion, we predict that temporary offspring desertion should be found especially among ectotherms, when periods of harsher environmental abiotic conditions for the parents are coincident with periods of low offspring demand for protection against predators. To take care of eggs is costly for the parents because they are exposed to predators or stressful environmental conditions. In order to avoid these costs, parents may leave the eggs temporarily unattended. Although temporary egg desertion has been reported for many species, the selective forces favoring its evolution are still poorly understood. Here, we investigated the costs and benefits of temporary egg desertion in a frog whose males care for eggs on rocky shores, an extreme environment for animals with permeable skin. Our findings lead us to conclude that temporary egg desertion should evolve when periods of harsher environmental conditions for the parents are coincident with periods of low offspring demand for protection against predators.

The expected quality of paternal behavior can influence female mating decisions and determine male mating success. We evaluated the importance of oviposition site quality, male body size, parental status (presence vs. absence of eggs under males’ protection), and time invested in care (less vs. more than 1 month) for male mating success in the harvestman Iporangaia pustulosa. The chances of acquiring a clutch are relatively small for noncaring males but increase nearly 4 times once males start caring for eggs. After 1 month of caring, the chances of acquiring an additional clutch show a marked decline, probably because the cumulative energetic costs imposed by paternal care decreases males’ attractiveness or their ability to replenish gametes throughout the caring period. Therefore, male mating success seems to be affected by a combination of presence of eggs and body condition while caring. Because the presence of eggs increases male attractiveness, we also conducted a field experiment removing caring males from their broods and expected that noncaring males would adopt unattended broods as a deceptive strategy to acquire matings. However, noncaring males cannibalized eggs and no brood adoption was recorded. Because well-fed males stay stationary on the vegetation waiting for mating opportunities, unattended broods may have been found more often by vagrant and poorly fed males. We argue that detailed comprehension of the costs and the benefits of paternal activities, as well as the direct benefits of female preference, is fundamental to better understand the interaction between male care and female mate choice.

Sperm competition theory has traditionally focused on how male allocation responds to female promiscuity, when males compete to fertilize a single clutch of eggs. Here, we develop a model to ask how female sperm use and storage across consecutive reproductive events affect male ejaculate allocation and patterns of mating and paternity. In our model, sperm use (a single parameter under female control) is the main determinant of sperm competition, which alters the effect of female promiscuity on male success and, ultimately, male reproductive allocation. Our theory reproduces the general pattern predicted by existing theory that increased sperm competition favors increased allocation to ejaculates. However, our model predicts a negative correlation between male ejaculate allocation and female promiscuity, challenging the generality of a prevailing expectation of sperm competition theory. Early models assumed that the energetic costs of precopulatory competition and the level of sperm competition are both determined by female promiscuity, which leads to an assumed covariation between these two processes. By modeling precopulatory costs and sperm competition independently, our theoretical framework allows us to examine how male allocation should respond independently to variation in sperm competition and energetic trade-offs in mating systems that have been overlooked in the past.

Paternal care has independently evolved in several arthropod lineages, but mating interactions have been described in detail for only a few species. Here, we describe the mating behavior of Iporangaia pustulosa, a Neotropical harvestman with exclusive paternal care. We obtained the data under natural conditions, and the results are based on 51 mating interactions. Females performed mate searching exclusively, locating and approaching stationary caring males on the vegetation. Upon arrival, nearly 33 % of the visiting females were promptly attacked and repelled by the males without copulating. We did not observe pre-copulatory courtship, and males, exclusively, performed copulatory courtship. Nearly 30 % of the females that copulated with caring males left the clutches without laying any egg. Finally, several behavioral actions reported here are remarkably similar to those observed in the sex-role-reversed harvestman Zygopachylus albomarginis, for which there is strong evidence of both male and female mate choice. In conclusion, our results provide evidence of male aggressive rejection of mates and female abandonment of clutches without ovipositing, suggesting that individuals of both sexes may evaluate and select mating partners.

Although the benefits of maternal care have been investigated in many species, the caring role of males in species with exclusive paternal care has received less attention. We experimentally quantified the protective role of paternal care in the harvestman Iporangaia pustulosa. Additionally, we compared the effectiveness of paternal care against predation in this species with a syntopic harvestman with maternal care, Acutisoma proximum. We demonstrated that nearly one-third of the unprotected Iporangaia clutches disappeared entirely in 12 days, while the other two-thirds suffered a mean reduction of 55% in egg number. Conversely, 50% of the control clutches did not suffer any reduction, and only one was entirely consumed by predators. We also demonstrated that the mucus coat that covers Iporangaia clutches has an important deterrent role against predation by conspecifics: 58.3% of the clutches without mucus were attacked and three of them were entirely consumed, whereas only three clutches with mucus were attacked, suffering a reduction of up to three eggs. Iporangaia males were as efficient as Acutisoma females in protecting eggs. However, unattended Acutisoma eggs were attacked 20% more frequently than unattended Iporangaia eggs. Unattended Iporangaia eggs are protected by a mucus coat that prevents or decreases predation rate, whereas Acutisoma eggs are more susceptible to predation, probably because they lack this mucus coat. Thus, besides the fact that Iporangaia males efficiently protect the offspring against egg predators, females also contribute to egg protection by providing a mucus coat that deters egg predators.

The objectives of this study were: (1) to test the existence of an aggregation pheromone in the gregarious psocid Cerastipsocus sivorii; (2) to compare the attractiveness of odors from different aggregations; (3) to test whether nymphs are able to chemically recognize damage-released alarm signals. In a choice experiment conducted in the laboratory, we showed that psocids are able to detect chemical cues from groups of conspecifics. Laboratory experiments also showed that nymphs are capable of chemically recognizing the aggregations where they came from. Finally, in a field experiment, most aggregations dispersed when exposed to the body fluids of a crushed conspecific, but no aggregations dispersed upon exposure to a crushed termite. The implications of these results for the evolution of sociality in psocopterans are discussed.

RESUmO Para se reproduzir, a maioria dos opilioes precisa passar por um longo processo, que envolve encontrar, selecionar e convencer um parceiro a copular, fertilizar os ovos, encontrar um local apropriado para oviposicao e, em algumas especies, proteger a prole. Em muitas especies de opilioes, o sistema de acasalamento se enquadra na definicao de poliginia por defesa de recursos, na qual os machos brigam pela posse de territorios que contem sitios de oviposicao preferidos pelas femeas. Em pelo menos uma especie, Acutisoma proximum , existe uma variacao descontinua no comprimento das pernas II, que sao sexualmente dimorficas e usadas pelos machos grandes como armas em brigas territoriais. Machos com pernas II curtas nao defendem territorios, mas adotam uma estrategia alternativa de acasalamento baseada na invasao de harens protegidos pelos machos grandes, onde eles conseguem copulas furtivas com as femeas. Apos a oviposicao, femeas de muitas especies pertencentes a superfamilia Gonyleptoidea cuidam dos ovos e das ninfas recem-eclodidas. Espera-se que o cuidado maternal em opilioes evolua apenas quando as femeas: (1) vivam o bastante para beneficiar a prole apos a oviposicao, (2) sejam capazes de defender a prole contra predadores e (3) restrinjam a reproducao a um unico evento durante uma estacao reprodutiva, de modo que elas obtenham um maior sucesso reprodutivo permanecendo com os ovos ate a eclosao das ninfas. Embora o cuidado maternal diminua a fecundidade total das femeas guardias, este comportamento e crucial para a sobrevivencia dos ovos, diminuindo a predacao por co-especificos e outros artropodes. Em pelo menos sete linhagens de opilioes pertencentes a subordem Laniatores, sao os machos que cuidam da prole. Enquanto o cuidado maternal provavelmente evoluiu como resultado de selecao natural, o cuidado paternal em opilioes parece ter evoluido como resultado de selecao sexual. Estudos experimentais demonstraram que machos que provem cuidado a prole sao preferidos pelas femeas e obtem um numero maior de copulas do que machos que nao provem cuidado. Adicionalmente, machos sem prole cuidam de desovas cujos pais foram removidos ― o que seria esperado dado que a presenca de ovos e atrativa para as femeas. A biologia reprodutiva dos opilioes e um tema fascinante e o grupo oferece uma oportunidade ideal para estudar selecao sexual em um clado diverso e pouco explorado pelos ecologos comportamentais. Palavras-chave : Selecao sexual, poliginia, estrategias alternativas de acasalamento, cuidado maternal, cuidado paternal.

Summary 1 Few studies have experimentally quantified the costs and benefits of female egg-guarding behaviour in arthropods under field conditions. Moreover, there is also a lack of studies assessing separately the survival and fecundity costs associated with this behavioural trait. 2 Here we employ field experimental manipulations and capture–mark–recapture methods to identify and quantify the costs and benefits of egg-guarding behaviour for females of the harvestman Acutisoma proximum Mello-Leitao, a maternal species from south-eastern Brazil. 3 In a female removal experiment that lasted 14 days, eggs left unattended under natural conditions survived 75·6% less than guarded eggs, revealing the importance of female presence preventing egg predation. 4 By monitoring females’ reproductive success for 2 years, we show that females experimentally prevented from guarding their eggs produced new clutches more frequently and had mean lifetime fecundity 18% higher than that of control guarding females. 5 Regarding survival, our capture–mark–recapture study does not show any difference between the survival rates of females prevented from caring and that of control guarding females. 6 We found that experimentally females prevented from guarding their eggs have a greater probability to produce another clutch (0·41) than females that cared for the offspring (0·34), regardless of their probability of surviving long enough to do that. 7 Our approach isolates the ecological costs of egg-guarding that would affect survival, such as increased risk of predation, and suggests that maternal egg-guarding also constrains fecundity through physiological costs of egg production. 8 Weighting costs and benefits of egg-guarding we demonstrate that the female's decision to desert would imply an average reduction of 73·3% in their lifetime fitness. Despite the verified fecundity costs of egg-guarding, this behaviour increases female fitness due to the crucial importance of female presence aimed to prevent egg predation.

Harvestmen belong to the order Opiliones , and, unlike other arachnids, they are highly polygynandrous , with both males and females mating multiply throughout the breeding season. In this chapter, we review the current information on sexual selection in the group, focusing mostly on intersexual interactions. Particularly, we provide an overview of harvestman mating systems, examine different temporal phases of male–female sexual interactions, and explore cases of sex role reversal . Several traits in harvestmen make them unique in the context of most previous studies of sexual selection. First, they have evolved an intromittent organ independently of other well-studied taxa, such as insects, spiders, and mammals. Second, the lack of long-range perception mechanisms reduces the window of opportunity for males and females to exchange information during the very short period between the first contact and intromission . In some cases, however, acceptance or rejection of a mate may be based on information gathered before contact, such as the quality of the male territory or the presence of eggs in his nest. Regardless of the role of pre-copulatory interactions, actual fertilization success is likely to be strongly dependent on the outcome of copulatory and post-copulatory processes. In this sense, the fact that most species are highly promiscuous and have sperm cells that lack flagella, which are stored near to the tip of the ovipositor and used to fertilize eggs immediately before oviposition, renders Opiliones a fertile ground to study the role of cryptic female choice, sperm competition, and sexual conflict.

Sperm competition games investigate how males partition limited resources between pre- and post-copulatory competition. Although extensive research has explored how various aspects of mating systems affect this allocation, male allocation between mating, fertilization and parental effort has not previously been considered. Yet, paternal care can be energetically expensive and males are generally predicted to adjust their parental effort in response to expected paternity. Here, we incorporate parental effort into sperm competition games, particularly exploring how the relationship between paternal care and offspring survival affects sperm competition and the relationship between paternity and paternal care. Our results support existing expectations that (i) fertilization effort should increase with female promiscuity and (ii) paternal care should increase with expected paternity. However, our analyses also reveal that the cost of male care can drive the strength of these patterns. When paternal behaviour is energetically costly, increased allocation to parental effort constrains allocation to fertilization effort. As paternal care becomes less costly, the association between paternity and paternal care weakens and may even be absent. By explicitly considering variation in sperm competition and the cost of male care, our model provides an integrative framework for predicting the interaction between paternal care and patterns of paternity.

Sperm competition theory has traditionally focused on how male allocation responds to female promiscuity, when males compete to fertilize a single clutch of eggs. Here, we develop a model to ask how female sperm use and storage across consecutive reproductive events affect male ejaculate allocation and patterns of mating and paternity. In our model, sperm use (a single parameter under female control) is the main determinant of sperm competition, which alters the effect of female promiscuity on male success and, ultimately, male reproductive allocation. Our theory reproduces the general pattern predicted by existing theory that increased sperm competition favors increased allocation to ejaculates. However, our model predicts a negative correlation between male ejaculate allocation and female promiscuity, challenging the generality of a prevailing expectation of sperm competition theory. Early models assumed that the energetic costs of precopulatory competition and the level of sperm competition are both determined by female promiscuity, which leads to an assumed covariation between these two processes. By modeling precopulatory costs and sperm competition independently, our theoretical framework allows us to examine how male allocation should respond independently to variation in sperm competition and energetic trade-offs in mating systems that have been overlooked in the past.

Exclusive paternal care is probably the rarest form of post-zygotic parental investment in nature. In arthropods, this behavior has independently evolved in 15 lineages, including approximately 1500 species. Here, we review the theoretical background for the evolution of parental investment and sex roles, contrasting classical views with the most recent mathematical models. Then, we introduce cases of exclusive paternal care in arthropods and explore empirical information, focusing on the costs and benefits of male egg guarding and the possible role of paternal care in male attractiveness and sex role reversal. Finally, we analyze the possible effects of temperature and rainfall on several ecological aspects that are likely to influence the evolution and maintenance of paternal care, and also derive specific macroecological predictions to be tested in future studies.

Nest-related behaviors may benefi t males by increasing off spring survival and their attractiveness to females, but may also limit males ’ foraging activity, increase their metabolic expenses, and expose them to increased mortality during nest attendance. Although intensively studied among birds and ectothermic vertebrates, the costs of nest-related behaviors in arthropods remain poorly explored. Females of the Neotropical harvestman Zygopachylus albomarginis (Arachnida: Opiliones) lay eggs exclusively inside mud nests that are built, repaired, cleaned and defended by males, which may remain stationary and associated with the nest for up to fi ve months. To assess energetic and survival costs of nest-related behaviors in this arthropod species, we measured body condition of nesting and non-nesting males and conducted a fi eld capturemark-recapture study to estimate their survival rates. Despite the long period of nest attendance, nesting males sustained good body conditions and presented higher survival rates than non-nesting males and females. Two ecological conditions may play an important role modulating the costs of nest attendance in the species. First, high food supply in tropical rainforests may provide males with frequent access to food in the vicinity of their nests, reducing or eliminating the costs related to limited foraging opportunities. Second, predation pressure seems to be directly mostly to vagrant individuals, so that the more they move, the more likely they are to be singled out by predators. Taken together, our fi ndings indicate that nest and off spring defense in Z. albomarginis provide numerous benefi ts, surprisingly imposing no evident cost to the males.

In arthropods, most cases of morphological dimorphism within males are the result of a conditional evolutionarily stable strategy (ESS) with status-dependent tactics. In conditionally male-dimorphic species, the status’ distributions of male morphs often overlap, and the environmentally cued threshold model (ET) states that the degree of overlap depends on the genetic variation in the distribution of the switchpoints that determine which morph is expressed in each value of status. Here we describe male dimorphism and alternative mating behaviors in the harvestman Serracutisoma proximum. Majors express elongated second legs and use them in territorial fights; minors possess short second legs and do not fight, but rather sneak into majors’ territories and copulate with egg-guarding females. The static allometry of second legs reveals that major phenotype expression depends on body size (status), and that the switchpoint underlying the dimorphism presents a large amount of genetic variation in the population, which probably results from weak selective pressure on this trait. With a mark-recapture study, we show that major phenotype expression does not result in survival costs, which is consistent with our hypothesis that there is weak selection on the switchpoint. Finally, we demonstrate that switchpoint is independent of status distribution. In conclusion, our data support the ET model prediction that the genetic correlation between status and switchpoint is low, allowing the status distribution to evolve or to fluctuate seasonally, without any effect on the position of the mean switchpoint.