Search

A small number of extraordinary “Major Evolutionary Transitions” (METs) have attracted attention among biologists. They comprise novel forms of individuality and information, and are defined in relation to organismal complexity, irrespective of broader ecosystem-level effects. This divorce between evolutionary and ecological consequences qualifies unicellular eukaryotes, for example, as a MET although they alone failed to significantly alter ecosystems. Additionally, this definition excludes revolutionary innovations not fitting into either MET type (e.g., photosynthesis). We recombine evolution with ecology to explore how and why entire ecosystems were newly created or radically altered – as Major System Transitions (MSTs). In doing so, we highlight important morphological adaptations that spread through populations because of their immediate, direct-fitness advantages for individuals. These are Major Competitive Transitions, or MCTs. We argue that often multiple METs and MCTs must be present to produce MSTs. For example, sexually-reproducing, multicellular eukaryotes (METs) with anisogamy and exoskeletons (MCTs) significantly altered ecosystems during the Cambrian. Therefore, we introduce the concepts of Facilitating Evolutionary Transitions (FETs) and Catalysts as key events or agents that are insufficient themselves to set a MST into motion, but are essential parts of synergies that do. We further elucidate the role of information in MSTs as transitions across five levels: (I) Encoded; (II) Epigenomic; (III) Learned; (IV) Inscribed; and (V) Dark Information. The latter is ‘authored’ by abiotic entities rather than biological organisms. Level IV has arguably allowed humans to produce a MST, and V perhaps makes us a FET for a future transition that melds biotic and abiotic life into one entity. Understanding the interactive processes involved in past major transitions will illuminate both current events and the surprising possibilities that abiotically-created inf

A small number of extraordinary “Major Evolutionary Transitions” (METs) have attracted attention among biologists. They comprise novel forms of individuality and information, and are defined in relation to organismal complexity, irrespective of broader ecosystem-level effects. This divorce between evolutionary and ecological consequences qualifies unicellular eukaryotes, for example, as a MET although they alone failed to significantly alter ecosystems. Additionally, this definition excludes revolutionary innovations not fitting into either MET type (e.g., photosynthesis). We recombine evolution with ecology to explore how and why entire ecosystems were newly created or radically altered – as Major System Transitions (MSTs). In doing so, we highlight important morphological adaptations that spread through populations because of their immediate, direct-fitness advantages for individuals. These are Major Competitive Transitions, or MCTs. We argue that often multiple METs and MCTs must be present to produce MSTs. For example, sexually-reproducing, multicellular eukaryotes (METs) with anisogamy and exoskeletons (MCTs) significantly altered ecosystems during the Cambrian. Therefore, we introduce the concepts of Facilitating Evolutionary Transitions (FETs) and Catalysts as key events or agents that are insufficient themselves to set a MST into motion, but are essential parts of synergies that do. We further elucidate the role of information in MSTs as transitions across five levels: (I) Encoded; (II) Epigenomic; (III) Learned; (IV) Inscribed; and (V) Dark Information. The latter is ‘authored’ by abiotic entities rather than biological organisms. Level IV has arguably allowed humans to produce a MST, and V perhaps makes us a FET for a future transition that melds biotic and abiotic life into one entity. Understanding the interactive processes involved in past major transitions will illuminate both current events and the surprising possibilities that abiotically-created inf

The reproductive (queen) and nonreproductive (worker) castes of eusocial insect colonies are a classic example of insect polyphenism. A complementary polyphenism may also exist entirely among females in the reproductive caste. Although less studied, reproductive females may vary in behavior based on size-associated attributes leading to the production of daughter workers. We studied a bee with flexible social behavior, Megalopta genalis, to better understand the potential of this polyphenism to shape the social organization of bee colonies and, by extension, its role in the evolution of eusociality. Our experimental design reduced variation among nest foundresses in life history variables that could influence reproductive decisions, such as nesting quality and early adulthood experience. Within our study population, approximately one third of M. genalis nests were eusocial and the remaining nests never produced workers. Though they do not differ in survival, nest-founding females who do not attempt to produce workers (which we refer to as the solitary phenotype) are significantly smaller and become reproductive later than females who attempt to recruit workers (the social phenotype). Females with the social phenotype are more likely to produce additional broods but at a cost of having some of their first offspring become nonreproductive workers. The likelihood of eusocial organization varies with body size across females of the social phenotype. Thus, fitness consequences associated with size-based plasticity in foundress behavior has colony level effects on eusociality. The potential for size-based polyphenisms among reproductive females may be an important factor to consider in the evolutionary origins of eusociality. © 2012 Springer-Verlag Berlin Heidelberg.

The reproductive (queen) and nonreproductive (worker) castes of eusocial insect colonies are a classic example of insect polyphenism. A complementary polyphenism may also exist entirely among females in the reproductive caste. Although less studied, reproductive females may vary in behavior based on size-associated attributes leading to the production of daughter workers. We studied a bee with flexible social behavior, Megalopta genalis, to better understand the potential of this polyphenism to shape the social organization of bee colonies and, by extension, its role in the evolution of eusociality. Our experimental design reduced variation among nest foundresses in life history variables that could influence reproductive decisions, such as nesting quality and early adulthood experience. Within our study population, approximately one third of M. genalis nests were eusocial and the remaining nests never produced workers. Though they do not differ in survival, nest-founding females who do not attempt to produce workers (which we refer to as the solitary phenotype) are significantly smaller and become reproductive later than females who attempt to recruit workers (the social phenotype). Females with the social phenotype are more likely to produce additional broods but at a cost of having some of their first offspring become nonreproductive workers. The likelihood of eusocial organization varies with body size across females of the social phenotype. Thus, fitness consequences associated with size-based plasticity in foundress behavior has colony level effects on eusociality. The potential for size-based polyphenisms among reproductive females may be an important factor to consider in the evolutionary origins of eusociality. © 2012 Springer-Verlag Berlin Heidelberg.

Infestations of buildings by Argentine ants, Linepithema humile (Mayr), were monitored on the campus of the University of California, Los Angeles. Foraging ant activity peaked during the hotter months of the year. The mean monthly maximum temperature, but not rainfall, positively correlated with indoor infestation frequency. Neither garden size nor the predominant groundcover vegetation correlated with the number of foraging ants at baits within gardens. Although the number of foraging ants outside a building varied over 40-fold, ant density in gardens did not predict the likelihood of infestation within the building. Also, the type of vegetative groundcover employed did not predict infestation frequency. There was, however, a significant negative relationship between the size of the garden outside of a building and the number of infestations. Given the large foraging area of L. humile workers, buildings next to small gardens may be infested simply because they lie within the "normal" foraging area of a colony. The best predictor of which rooms were infested within buildings was the presence of a water source. Thus providing water for ant colonies outside and away from buildings may be one method of integrated pest management to reduce the proclivity of ants to infest structures. Copyright © 2012 Smadar Gilboa et al.

Infestations of buildings by Argentine ants, Linepithema humile (Mayr), were monitored on the campus of the University of California, Los Angeles. Foraging ant activity peaked during the hotter months of the year. The mean monthly maximum temperature, but not rainfall, positively correlated with indoor infestation frequency. Neither garden size nor the predominant groundcover vegetation correlated with the number of foraging ants at baits within gardens. Although the number of foraging ants outside a building varied over 40-fold, ant density in gardens did not predict the likelihood of infestation within the building. Also, the type of vegetative groundcover employed did not predict infestation frequency. There was, however, a significant negative relationship between the size of the garden outside of a building and the number of infestations. Given the large foraging area of L. humile workers, buildings next to small gardens may be infested simply because they lie within the "normal" foraging area of a colony. The best predictor of which rooms were infested within buildings was the presence of a water source. Thus providing water for ant colonies outside and away from buildings may be one method of integrated pest management to reduce the proclivity of ants to infest structures. Copyright © 2012 Smadar Gilboa et al.

Ants exhibit a size-associated colony founding trait that is characterized by the degree to which foundresses rely on internal reserves to raise their first brood of workers (claustrality). The reliance on stored reserves is positively correlated with degree of claustrality (claustral > facultative > semi-claustral) and is variable across species of Pogonomyrmex harvester ants. Three species of harvester ant foundresses that differ in degree of claustrality were observed initiating nests under laboratory conditions over 2 years. P. rugosus is fully claustral, P. salinus is facultative, and P. californicus is semi-claustral. Across species, degree of claustrality was positively associated with mean digging rate and nest depth over the first 3 days of nest initiation, total nest depth, and degree of nest closure. Branching and abundance of peripheral nodes were higher in semi-claustral and facultative nests than in claustral nests. The facultative species dug for the longest time and achieved the greatest tunnel length. Within each species, there were trends associating mass with digging rate, but these were not consistent in all species. There were no intraspecific trends of mass with nest depth. Also within species, a foundress’s mass did not affect her tendency to open or close her nest. These results reveal degree of claustrality is correlated across species with several nest initiation characteristics that together may represent different colony founding syndromes.

The velvety tree ant (Liometopum occidental Emery) is a dominant ant species found in Californian pine and oak woodlands. We performed a series of experiments to examine the degree of intraspecific aggression between nests. Within a site locality, ants collected from distances over a kilometer apart showed no aggression. However, ants from separate sites (more than 150 km apart) were strongly aggressive towards each other. Observation of food collection from baits further showed that L. occidentale trails can exceed over 70m. These combined observations suggest that L. occidentale has a natural life history that exhibits unicoloniality with perhaps the formation of large, habitat-dominating supercolonies. We also report an observation of a mating flight of L. occidentale that suggests females do disperse from their natal nests.

Ants exhibit a size-associated colony founding trait that is characterized by the degree to which foundresses rely on internal reserves to raise their first brood of workers (claustrality). The reliance on stored reserves is positively correlated with degree of claustrality (claustral > facultative > semi-claustral) and is variable across species of Pogonomyrmex harvester ants. Three species of harvester ant foundresses that differ in degree of claustrality were observed initiating nests under laboratory conditions over 2 years. P. rugosus is fully claustral, P. salinus is facultative, and P. californicus is semi-claustral. Across species, degree of claustrality was positively associated with mean digging rate and nest depth over the first 3 days of nest initiation, total nest depth, and degree of nest closure. Branching and abundance of peripheral nodes were higher in semi-claustral and facultative nests than in claustral nests. The facultative species dug for the longest time and achieved the greatest tunnel length. Within each species, there were trends associating mass with digging rate, but these were not consistent in all species. There were no intraspecific trends of mass with nest depth. Also within species, a foundress’s mass did not affect her tendency to open or close her nest. These results reveal degree of claustrality is correlated across species with several nest initiation characteristics that together may represent different colony founding syndromes.

The velvety tree ant (Liometopum occidental Emery) is a dominant ant species found in Californian pine and oak woodlands. We performed a series of experiments to examine the degree of intraspecific aggression between nests. Within a site locality, ants collected from distances over a kilometer apart showed no aggression. However, ants from separate sites (more than 150 km apart) were strongly aggressive towards each other. Observation of food collection from baits further showed that L. occidentale trails can exceed over 70m. These combined observations suggest that L. occidentale has a natural life history that exhibits unicoloniality with perhaps the formation of large, habitat-dominating supercolonies. We also report an observation of a mating flight of L. occidentale that suggests females do disperse from their natal nests.

In group-living animals reproduction is often skewed such that some group members reproduce more than others. In addition to reproductive skew, group members may also exhibit social skew, where some individuals show particular behaviors more often than others. Significant social skew in behaviors such as anti-predator defense or social interactions may influence survival and reproduction. Therefore, social skew has the potential to translate into reproductive skew and affect group productivity. We measured social skew across groups in a population of yellow-bellied marmots (Marmota flaviventris). Several behaviors such as agonistic interactions, affiliative interactions, and first emergence were significantly skewed in most groups. Alarm calling, however, was infrequently skewed more than would be expected by random chance. Thus, marmot groups do not appear to have behavioral roles in terms of individuals acting like sentinels. Although significant social skew was present, it did not obviously affect fitness as measured by female reproductive success for each group. However, skew in individual-directed behavior (e.g. agonistic and affiliative interactions) did significantly correlate with the level of reproductive skew. Finally, the results were independent of the scale at which groups were defined. Behavioral variability appears to occur similarly across the entire marmot population. The results of this study illustrate that the quantification of social skew has potential to be a powerful tool for understanding the evolution of sociality.Introduction.Animal groups are characterized by variation in the degree to which individuals exhibit specific behaviors and variance across group members in the distribution of such variables has come to be called “skew” (Reeve Ratnieks 1993, Keller Reeve 1994, Ruzzante et al. 1995, Kokko Lindström 1997, Kokko et al. 1999, Nonacs 2000).

In group-living animals reproduction is often skewed such that some group members reproduce more than others. In addition to reproductive skew, group members may also exhibit social skew, where some individuals show particular behaviors more often than others. Significant social skew in behaviors such as anti-predator defense or social interactions may influence survival and reproduction. Therefore, social skew has the potential to translate into reproductive skew and affect group productivity. We measured social skew across groups in a population of yellow-bellied marmots (Marmota flaviventris). Several behaviors such as agonistic interactions, affiliative interactions, and first emergence were significantly skewed in most groups. Alarm calling, however, was infrequently skewed more than would be expected by random chance. Thus, marmot groups do not appear to have behavioral roles in terms of individuals acting like sentinels. Although significant social skew was present, it did not obviously affect fitness as measured by female reproductive success for each group. However, skew in individual-directed behavior (e.g. agonistic and affiliative interactions) did significantly correlate with the level of reproductive skew. Finally, the results were independent of the scale at which groups were defined. Behavioral variability appears to occur similarly across the entire marmot population. The results of this study illustrate that the quantification of social skew has potential to be a powerful tool for understanding the evolution of sociality.Introduction.Animal groups are characterized by variation in the degree to which individuals exhibit specific behaviors and variance across group members in the distribution of such variables has come to be called “skew” (Reeve Ratnieks 1993, Keller Reeve 1994, Ruzzante et al. 1995, Kokko Lindström 1997, Kokko et al. 1999, Nonacs 2000).

We observed aggregations of the sand wasp, Steniolia nigripes, in the Granite Mountains of Southern California. Males gathered in open areas between bushes in a sun-dancing behavior very close to the ground. They did not hold exclusive territories. Aggregations were highly visible, but occurred at low densities in the area. Males often chased each other and females, who would approach the aggregation, then leave with males following closely or attached to her. Females often burrowed around the edges of the aggregation. We captured and measured male and female head width, dry weight and thorax length. Males were significantly larger than females in all of these measurements. Intrasexual selection resulting from scramble competition for access to mates may drive this dimorphism. As these aggregations did not occur at obvious landmarks, it is possible that the aggregations themselves serve as a landmarks for females.

We observed aggregations of the sand wasp, Steniolia nigripes, in the Granite Mountains of Southern California. Males gathered in open areas between bushes in a sun-dancing behavior very close to the ground. They did not hold exclusive territories. Aggregations were highly visible, but occurred at low densities in the area. Males often chased each other and females, who would approach the aggregation, then leave with males following closely or attached to her. Females often burrowed around the edges of the aggregation. We captured and measured male and female head width, dry weight and thorax length. Males were significantly larger than females in all of these measurements. Intrasexual selection resulting from scramble competition for access to mates may drive this dimorphism. As these aggregations did not occur at obvious landmarks, it is possible that the aggregations themselves serve as a landmarks for females.

Although theories of parental investment and sex ratio generally assume that a single resource limits reproduction, many organisms invest two or more qualitatively different types of resources in the production of offspring. We examine the consequences of multifaceted parental investment for offspring provisioning and sex allocation, building our argument around a study of the nest-building Hymenoptera (wasps, bees, and ants). We review empirical studies that demonstrate that lifetime reproductive success may be constrained not only by resources used to provision offspring but also by the supply of mature oocytes or, in some cases, by the availability of space within nest sites or the time required to defend nests. Under multifaceted parental investment, the factor limiting parental fitness determines the currency of the optimization problem; parents are predicted to adjust reproductive behavior to maximize fitness returns per unit of the limiting resource. We develop simple models that predict that a greater availability of resources used for provisions will lead to an increase in the amount provisioned per offspring and an increase in the numerical or biomass proportion of females produced. These predictions explain widely observed patterns of variation in offspring provisioning and sex allocation in the nest-building Hymenoptera.

Although theories of parental investment and sex ratio generally assume that a single resource limits reproduction, many organisms invest two or more qualitatively different types of resources in the production of offspring. We examine the consequences of multifaceted parental investment for offspring provisioning and sex allocation, building our argument around a study of the nest-building Hymenoptera (wasps, bees, and ants). We review empirical studies that demonstrate that lifetime reproductive success may be constrained not only by resources used to provision offspring but also by the supply of mature oocytes or, in some cases, by the availability of space within nest sites or the time required to defend nests. Under multifaceted parental investment, the factor limiting parental fitness determines the currency of the optimization problem; parents are predicted to adjust reproductive behavior to maximize fitness returns per unit of the limiting resource. We develop simple models that predict that a greater availability of resources used for provisions will lead to an increase in the amount provisioned per offspring and an increase in the numerical or biomass proportion of females produced. These predictions explain widely observed patterns of variation in offspring provisioning and sex allocation in the nest-building Hymenoptera.