Brain compartment size allometries may adaptively reflect cognitive needs associated with behavio... more Brain compartment size allometries may adaptively reflect cognitive needs associated with behavioral development and ecology. Ants provide an informative system to study the relationship of neural architecture and development because worker tasks and sensory inputs may change with age. Additionally, tasks may be divided among morphologically and behaviorally differentiated worker groups (subcastes), reducing repertoire size through specialization and aligning brain structure with task-specific cognitive requirements. We hypothesized that division of labor may decrease developmental neuroplasticity in workers due to the apparently limited behavioral flexibility associated with task specialization. To test this hypothesis, we compared macroscopic and cellular neuroanatomy in two ant sister clades with striking contrasts in worker morphological differentiation and colony-level social organization: Oecophylla smaragdina, a socially complex species with large colonies and behaviorally di...
The metabolic expense of producing and operating neural tissue required for adaptive behaviour is... more The metabolic expense of producing and operating neural tissue required for adaptive behaviour is considered a significant selective force in brain evolution. In primates, brain size correlates positively with group size, presumably owing to the greater cognitive demands of complex social relationships in large societies. Social complexity in eusocial insects is also associated with large groups, as well as collective intelligence and division of labour among sterile workers. However, superorganism phenotypes may lower cognitive demands on behaviourally specialized workers resulting in selection for decreased brain size and/or energetic costs of brain metabolism. To test this hypothesis, we compared brain investment patterns and cytochrome oxidase (COX) activity, a proxy for ATP usage, in two ant species contrasting in social organization. Socially complex Oecophylla smaragdina workers had larger brain size and relative investment in the mushroom bodies (MBs)-higher order sensory pr...
Understanding how the environment influences patterns of diversity is vital for effective conserv... more Understanding how the environment influences patterns of diversity is vital for effective conservation management, especially in a changing global climate. While assemblage structure and species richness patterns are often correlated with current environmental factors, historical influences may also be considerable, especially for taxa with poor dispersal abilities. Mountain-top regions throughout tropical rainforests can act as important refugia for taxa characterised by low dispersal capacities such as flightless ground beetles (Carabidae), an ecologically significant predatory group. We surveyed flightless ground beetles along elevational gradients in five different subregions within the Australian Wet Tropics World Heritage Area to investigate (1) whether the diversity and composition of flightless ground beetles are elevationally stratified, and, if so, (2) what environmental factors (other than elevation per se) are associated with these patterns. Generalised linear models and...
Over the last year, our flying-fox research team in North Queensland has observed evidence of all... more Over the last year, our flying-fox research team in North Queensland has observed evidence of all four Australian Pteropus species (Pteropus alecto, P. conspicillatus, P. poliocephalus and P. scapulatus) co-roosting at a single camp near Mackay. Amusingly/Interestingly, this unique camp also happens to be located on a property that hosts a 'flying-fox' eco-tourism operation. 'Forest Flying' at Finch Hatton offers an opportunity to observe the species' composition of this flying-fox camp by meeting our favourite critters eye-to-eye while suspended in the rainforest canopy about 25m above the forest floor (see photo). Owners and commercial operators Dave and Donna Lowe kindly brought this amazing flying-fox camp to our attention. As keen naturalists, they have been meticulously recording details of the comings and goings of different flying-fox species since 2005. Perhaps their slogan should really be "Flying-foxes R Us!". We would like to thank Dave and ...
The fine structure of epididymal or electro-ejaculated spermatozoa of Pteropus poliocephalus, P. ... more The fine structure of epididymal or electro-ejaculated spermatozoa of Pteropus poliocephalus, P. scapulatus, P. conspiculatus, P. alecto and Syconycteris australis is described. The sperm of all species were found to be very similar. The head is extremely flattened and spatulate; the nucleus is capped by a long acrosome that comprises the proximal half of the head and covers two-thirds of the nucleus area, and a prominent sub-acrosomal space possesses a unique 'anvil'-like shape. Redundant nuclear envelope forms a 'scroll' in a restricted region of the neck, next to the base of the proximal centriole and the most proximal of the mitochondria. The axoneme is atypical for mammals, the central singlets arising distal to the outer doublets. Coarse fibres 1, 5, 6 and 9 are larger than the remainder, a feature shared with the Microchiroptera, most insectivores and the Primates. The large sub-acrosomal space of the megachiropteran sperm is significantly is different from th...
Here we provide an update on the batting activities of the James Cook University’s biannual under... more Here we provide an update on the batting activities of the James Cook University’s biannual undergraduate field trip to Danum Valley Field Centre in Borneo. The 2013 trip focussed on various bat surveying techniques, with an emphasis on the use and effectiveness of the EM3 full-spectrum and Anabat II ZCAM ultrasonic detectors. We captured a total of thirty-three individuals of 12 different species in harp traps and mist nets, three species of which had not been encountered on previous surveys. We collected an additional 16,500 call files and in total, we now have a call library of 43 microbat species (of which 28 can be allocated to individual species) along with high-quality photographs of 20 micro- and megabats. It will be no surprise that Terry Reardon also took dynamic photographs of individuals in flight upon release, and generously donated his flash-setup to the staff of Danum Valley. Future field trips will continue to build the call and photo library as well as collect tissu...
A complete guide to the statistical analysis of Whitlock & Schluter's The Analysis of Biuolog... more A complete guide to the statistical analysis of Whitlock & Schluter's The Analysis of Biuological Data, using SPlus statistical analysis software. With a few extra things thrown in . . .mixed models, ANCOVA, Repeated Measures . .
Weaver ants are unique among ants in forming chains of living workers to bridge gaps in the canop... more Weaver ants are unique among ants in forming chains of living workers to bridge gaps in the canopy. Together, they are capable of making collective decisions when faced with a binary choice of gaps, with chains more likely to bridge the gap between a closer than distant, or larger rather than smaller, target. Although the recruitment dynamics looks identical to that of mass recruiting ants when faced with two food choices, the entire process appears to occur in the complete absence of individual communication or recruitment. Rather, the process is driven by the time at which work commences: the probability of chain initiation at the relevant work site. Flow rates in and out of chains are constant and irrespective of the target type and remain constant once work commences: switching targets in the middle of a choice has no effect on chain dynamics. The probability that a chain forms to a particular target appears to be determined by the optical image size of the target to individual ants. Ants are more likely to bridge a gap to larger rather than smaller targets that are at the same distance, and to closer rather than more distant targets of similar size, but they show no preferences when offered a pairwise choice between two targets with the same visual angle but differing in size and distance. Efforts to replicate collective decision-making in other systems may not require the parallel development of communication and recruitment systems.
The number of queens per colony and the number of matings per queen are the most important determ... more The number of queens per colony and the number of matings per queen are the most important determinants of the genetic structure of ant colonies, and understanding their interrelationship is essential to the study of social evolution. The polygyny-vs.-polyandry hypothesis argues that polygyny and polyandry should be negatively associated because both can result in increased intracolonial genetic variability and have costs. However, evidence for this long-debated hypothesis has been lacking at the intraspecific level. Here, we investigated the colony genetic structure in the Australian bulldog ant Myrmecia brevinoda. The numbers of queens per colony varied from 1 to 6. Nestmate queens within polygynous colonies were on average related (r qq = 0.171 ± 0.019), but the overall relatedness between queens and their mates was indistinguishable from zero (r qm = 0.037 ± 0.030). Queens were inferred to mate with 1-10 males. A lack of genetic isolation by distance among nests indicated the prevalence of independent colony foundation. In accordance with the polygyny-vs.-polyandry hypothesis, the number of queens per colony was significantly negatively associated with the estimated number of matings (Spearman rank correlation R =)0.490, P = 0.028). This study thus provides the rare intraspecific evidence for the polygyny-vs.-polyandry hypothesis. We suggest that the high costs of multiple matings and the strong effect of multiple mating on intracolonial genetic diversity may be essential to the negative association between polygyny and polyandry and that any attempt to empirically test this hypothesis should place emphasis upon these two key underlying aspects.
Context Fire is a major ecological factor in many landscapes. Prescribed fires are often used in ... more Context Fire is a major ecological factor in many landscapes. Prescribed fires are often used in the management of vegetation for ecological values, wildlife habitat and reduction of risk of wildfire. However, debate continues over whether active fire management is beneficial to flora and fauna. Although bats comprise ~20% of the world’s extant mammal fauna, they have been largely ignored in studies investigating ecosystem response to fire, especially in Australia. Aims In the present study, we aim to investigate the immediate responses of microbats to prescribed fires in a tropical eucalypt woodland.Methods We used a replicated paired experimental design, consisting of burned and unburned treatment and control sites, to investigate how bat activity and community structure change following a prescribed fire. Key results Total bat activity increased significantly following fire. Fire also resulted in changes in the bat species assemblage. Changes in community structure were driven by...
We investigated patterns of community structure (species composition, foraging activity, and nigh... more We investigated patterns of community structure (species composition, foraging activity, and nightly foraging patterns) of bats in relation to gradients of environmental variation in a tropical urban area. A total of 32 sites spread equally across eight habitat types were sampled in the city of Townsville, North Queensland, Australia. Each site was sampled on 3 non-consecutive occasions using automated AnaBat systems. Eleven species were confidently identified while a possible four more were identified only to the genus level. Ordination of environmental variables measured at these sites identified two distinct environmental gradients reflecting the degree of urbanisation and foliage density. With increasing urbanisation there was a decline in species richness and total foraging activity. We used regression trees to characterise foraging preferences of each species. This analysis suggested that only one species of Mormopterus was able to exploit the resources provided by urbanisation. This species foraged in areas with higher numbers of white streetlights. The remaining species of bats preferred to forage within close proximity to natural vegetation and with low numbers of streetlights. The density of vegetation in long-established suburbs did not substantially reverse the trend for urban areas to have fewer bat species than original habitats.
Polyrhachis ants represent one of the most taxonomically and ecologically diverse ant genera, wit... more Polyrhachis ants represent one of the most taxonomically and ecologically diverse ant genera, with over 500 described species organised into 12 subgenera. Nesting habits range from subterranean localities to arboreal nests incorporating silk produced by the ants' own larvae (nest weaving). In this article, we combine scanning electron microscopy and gross observations of the nests of 35 species representing nine subgenera thought to contain individuals that nest above the ground (Cyrtomyrma, Hagiomyrma, Hedomyrma, Hemioptica, Myrma, Myrmatopa, Myrmhopla, Myrmothrinax, Polyrhachis) to revaluate the relationship between nest locale, the type of nest material used and the use of larval silk for nest construction. Nesting habits are highly diverse, ranging from truly arboreal nests on or between leaves and branches, to lignicolous nests inside hollow stems or bamboo internodes and lithocolous nests on the sides of rock walls. Flat sheets of larval silk are used only by arboreal nesting species within the subgenera Cyrtomyrma , Hemioptica , Myrma , Myrmatopa , Myrmothrinax and Polyrhachis. Lignicolous nesting habits were demonstrated predominantly by Hedomyrma spp., but these habits also occur in Myrma and Myrmhopla. Lithicolous nesting habits occur within Hagiomyrma and Hedomyrma , though the actual nesting material used can be either carton or dense masses of spider silk. Based on existing phylogenetic hypotheses, the use of larval silk for nest construction has evolved independently within the genus, and has evolved independently of the construction of silk nests per se. Further examination of the exact type of silk found in the colonies of 'nest-weaving' Polyrhachis is warranted.
Brain compartment size allometries may adaptively reflect cognitive needs associated with behavio... more Brain compartment size allometries may adaptively reflect cognitive needs associated with behavioral development and ecology. Ants provide an informative system to study the relationship of neural architecture and development because worker tasks and sensory inputs may change with age. Additionally, tasks may be divided among morphologically and behaviorally differentiated worker groups (subcastes), reducing repertoire size through specialization and aligning brain structure with task-specific cognitive requirements. We hypothesized that division of labor may decrease developmental neuroplasticity in workers due to the apparently limited behavioral flexibility associated with task specialization. To test this hypothesis, we compared macroscopic and cellular neuroanatomy in two ant sister clades with striking contrasts in worker morphological differentiation and colony-level social organization: Oecophylla smaragdina, a socially complex species with large colonies and behaviorally di...
The metabolic expense of producing and operating neural tissue required for adaptive behaviour is... more The metabolic expense of producing and operating neural tissue required for adaptive behaviour is considered a significant selective force in brain evolution. In primates, brain size correlates positively with group size, presumably owing to the greater cognitive demands of complex social relationships in large societies. Social complexity in eusocial insects is also associated with large groups, as well as collective intelligence and division of labour among sterile workers. However, superorganism phenotypes may lower cognitive demands on behaviourally specialized workers resulting in selection for decreased brain size and/or energetic costs of brain metabolism. To test this hypothesis, we compared brain investment patterns and cytochrome oxidase (COX) activity, a proxy for ATP usage, in two ant species contrasting in social organization. Socially complex Oecophylla smaragdina workers had larger brain size and relative investment in the mushroom bodies (MBs)-higher order sensory pr...
Understanding how the environment influences patterns of diversity is vital for effective conserv... more Understanding how the environment influences patterns of diversity is vital for effective conservation management, especially in a changing global climate. While assemblage structure and species richness patterns are often correlated with current environmental factors, historical influences may also be considerable, especially for taxa with poor dispersal abilities. Mountain-top regions throughout tropical rainforests can act as important refugia for taxa characterised by low dispersal capacities such as flightless ground beetles (Carabidae), an ecologically significant predatory group. We surveyed flightless ground beetles along elevational gradients in five different subregions within the Australian Wet Tropics World Heritage Area to investigate (1) whether the diversity and composition of flightless ground beetles are elevationally stratified, and, if so, (2) what environmental factors (other than elevation per se) are associated with these patterns. Generalised linear models and...
Over the last year, our flying-fox research team in North Queensland has observed evidence of all... more Over the last year, our flying-fox research team in North Queensland has observed evidence of all four Australian Pteropus species (Pteropus alecto, P. conspicillatus, P. poliocephalus and P. scapulatus) co-roosting at a single camp near Mackay. Amusingly/Interestingly, this unique camp also happens to be located on a property that hosts a 'flying-fox' eco-tourism operation. 'Forest Flying' at Finch Hatton offers an opportunity to observe the species' composition of this flying-fox camp by meeting our favourite critters eye-to-eye while suspended in the rainforest canopy about 25m above the forest floor (see photo). Owners and commercial operators Dave and Donna Lowe kindly brought this amazing flying-fox camp to our attention. As keen naturalists, they have been meticulously recording details of the comings and goings of different flying-fox species since 2005. Perhaps their slogan should really be "Flying-foxes R Us!". We would like to thank Dave and ...
The fine structure of epididymal or electro-ejaculated spermatozoa of Pteropus poliocephalus, P. ... more The fine structure of epididymal or electro-ejaculated spermatozoa of Pteropus poliocephalus, P. scapulatus, P. conspiculatus, P. alecto and Syconycteris australis is described. The sperm of all species were found to be very similar. The head is extremely flattened and spatulate; the nucleus is capped by a long acrosome that comprises the proximal half of the head and covers two-thirds of the nucleus area, and a prominent sub-acrosomal space possesses a unique 'anvil'-like shape. Redundant nuclear envelope forms a 'scroll' in a restricted region of the neck, next to the base of the proximal centriole and the most proximal of the mitochondria. The axoneme is atypical for mammals, the central singlets arising distal to the outer doublets. Coarse fibres 1, 5, 6 and 9 are larger than the remainder, a feature shared with the Microchiroptera, most insectivores and the Primates. The large sub-acrosomal space of the megachiropteran sperm is significantly is different from th...
Here we provide an update on the batting activities of the James Cook University’s biannual under... more Here we provide an update on the batting activities of the James Cook University’s biannual undergraduate field trip to Danum Valley Field Centre in Borneo. The 2013 trip focussed on various bat surveying techniques, with an emphasis on the use and effectiveness of the EM3 full-spectrum and Anabat II ZCAM ultrasonic detectors. We captured a total of thirty-three individuals of 12 different species in harp traps and mist nets, three species of which had not been encountered on previous surveys. We collected an additional 16,500 call files and in total, we now have a call library of 43 microbat species (of which 28 can be allocated to individual species) along with high-quality photographs of 20 micro- and megabats. It will be no surprise that Terry Reardon also took dynamic photographs of individuals in flight upon release, and generously donated his flash-setup to the staff of Danum Valley. Future field trips will continue to build the call and photo library as well as collect tissu...
A complete guide to the statistical analysis of Whitlock & Schluter's The Analysis of Biuolog... more A complete guide to the statistical analysis of Whitlock & Schluter's The Analysis of Biuological Data, using SPlus statistical analysis software. With a few extra things thrown in . . .mixed models, ANCOVA, Repeated Measures . .
Weaver ants are unique among ants in forming chains of living workers to bridge gaps in the canop... more Weaver ants are unique among ants in forming chains of living workers to bridge gaps in the canopy. Together, they are capable of making collective decisions when faced with a binary choice of gaps, with chains more likely to bridge the gap between a closer than distant, or larger rather than smaller, target. Although the recruitment dynamics looks identical to that of mass recruiting ants when faced with two food choices, the entire process appears to occur in the complete absence of individual communication or recruitment. Rather, the process is driven by the time at which work commences: the probability of chain initiation at the relevant work site. Flow rates in and out of chains are constant and irrespective of the target type and remain constant once work commences: switching targets in the middle of a choice has no effect on chain dynamics. The probability that a chain forms to a particular target appears to be determined by the optical image size of the target to individual ants. Ants are more likely to bridge a gap to larger rather than smaller targets that are at the same distance, and to closer rather than more distant targets of similar size, but they show no preferences when offered a pairwise choice between two targets with the same visual angle but differing in size and distance. Efforts to replicate collective decision-making in other systems may not require the parallel development of communication and recruitment systems.
The number of queens per colony and the number of matings per queen are the most important determ... more The number of queens per colony and the number of matings per queen are the most important determinants of the genetic structure of ant colonies, and understanding their interrelationship is essential to the study of social evolution. The polygyny-vs.-polyandry hypothesis argues that polygyny and polyandry should be negatively associated because both can result in increased intracolonial genetic variability and have costs. However, evidence for this long-debated hypothesis has been lacking at the intraspecific level. Here, we investigated the colony genetic structure in the Australian bulldog ant Myrmecia brevinoda. The numbers of queens per colony varied from 1 to 6. Nestmate queens within polygynous colonies were on average related (r qq = 0.171 ± 0.019), but the overall relatedness between queens and their mates was indistinguishable from zero (r qm = 0.037 ± 0.030). Queens were inferred to mate with 1-10 males. A lack of genetic isolation by distance among nests indicated the prevalence of independent colony foundation. In accordance with the polygyny-vs.-polyandry hypothesis, the number of queens per colony was significantly negatively associated with the estimated number of matings (Spearman rank correlation R =)0.490, P = 0.028). This study thus provides the rare intraspecific evidence for the polygyny-vs.-polyandry hypothesis. We suggest that the high costs of multiple matings and the strong effect of multiple mating on intracolonial genetic diversity may be essential to the negative association between polygyny and polyandry and that any attempt to empirically test this hypothesis should place emphasis upon these two key underlying aspects.
Context Fire is a major ecological factor in many landscapes. Prescribed fires are often used in ... more Context Fire is a major ecological factor in many landscapes. Prescribed fires are often used in the management of vegetation for ecological values, wildlife habitat and reduction of risk of wildfire. However, debate continues over whether active fire management is beneficial to flora and fauna. Although bats comprise ~20% of the world’s extant mammal fauna, they have been largely ignored in studies investigating ecosystem response to fire, especially in Australia. Aims In the present study, we aim to investigate the immediate responses of microbats to prescribed fires in a tropical eucalypt woodland.Methods We used a replicated paired experimental design, consisting of burned and unburned treatment and control sites, to investigate how bat activity and community structure change following a prescribed fire. Key results Total bat activity increased significantly following fire. Fire also resulted in changes in the bat species assemblage. Changes in community structure were driven by...
We investigated patterns of community structure (species composition, foraging activity, and nigh... more We investigated patterns of community structure (species composition, foraging activity, and nightly foraging patterns) of bats in relation to gradients of environmental variation in a tropical urban area. A total of 32 sites spread equally across eight habitat types were sampled in the city of Townsville, North Queensland, Australia. Each site was sampled on 3 non-consecutive occasions using automated AnaBat systems. Eleven species were confidently identified while a possible four more were identified only to the genus level. Ordination of environmental variables measured at these sites identified two distinct environmental gradients reflecting the degree of urbanisation and foliage density. With increasing urbanisation there was a decline in species richness and total foraging activity. We used regression trees to characterise foraging preferences of each species. This analysis suggested that only one species of Mormopterus was able to exploit the resources provided by urbanisation. This species foraged in areas with higher numbers of white streetlights. The remaining species of bats preferred to forage within close proximity to natural vegetation and with low numbers of streetlights. The density of vegetation in long-established suburbs did not substantially reverse the trend for urban areas to have fewer bat species than original habitats.
Polyrhachis ants represent one of the most taxonomically and ecologically diverse ant genera, wit... more Polyrhachis ants represent one of the most taxonomically and ecologically diverse ant genera, with over 500 described species organised into 12 subgenera. Nesting habits range from subterranean localities to arboreal nests incorporating silk produced by the ants' own larvae (nest weaving). In this article, we combine scanning electron microscopy and gross observations of the nests of 35 species representing nine subgenera thought to contain individuals that nest above the ground (Cyrtomyrma, Hagiomyrma, Hedomyrma, Hemioptica, Myrma, Myrmatopa, Myrmhopla, Myrmothrinax, Polyrhachis) to revaluate the relationship between nest locale, the type of nest material used and the use of larval silk for nest construction. Nesting habits are highly diverse, ranging from truly arboreal nests on or between leaves and branches, to lignicolous nests inside hollow stems or bamboo internodes and lithocolous nests on the sides of rock walls. Flat sheets of larval silk are used only by arboreal nesting species within the subgenera Cyrtomyrma , Hemioptica , Myrma , Myrmatopa , Myrmothrinax and Polyrhachis. Lignicolous nesting habits were demonstrated predominantly by Hedomyrma spp., but these habits also occur in Myrma and Myrmhopla. Lithicolous nesting habits occur within Hagiomyrma and Hedomyrma , though the actual nesting material used can be either carton or dense masses of spider silk. Based on existing phylogenetic hypotheses, the use of larval silk for nest construction has evolved independently within the genus, and has evolved independently of the construction of silk nests per se. Further examination of the exact type of silk found in the colonies of 'nest-weaving' Polyrhachis is warranted.
Uploads
Papers by Simon Robson