SPATIAL DISTRIBUTION OF A PRIMITIVELY SOCIAL BEE: DOES GENETIC POPULATION STRUCTURE FACILITATE ALTRUISM?

Exoneura bicolor is a univoltine, facultatively social bee exhibiting a solitary/quasisocial/semisocial colony polymorphism (Schwarz, 1986, 1987). Intracolony relatedness in semisocial colonies has been previously estimated at 0.49 ± 0.06 (Schwarz, 1987), although the crucial relatedness between altruists and the brood that they rear will be about half this value. This value is unlikely to be increased by the preferential rearing of only close relatives (Schwarz, 1988a) and no known morphological specializations preclude workers from reproducing in this species. Hamilton (1972, 1975) suggested that relatedness may be increased through population subdivision, if this leads to significant inbreeding and increased between-colony genetic variance. The same process may also operate at higher levels of population structure (e.g., Wade, 1978). Population structure and intracolony relatedness in E. bicolor were investigated in seven localities in southern Victoria, Australia, to determine if inbreeding at any level of population structure was contributing to relatedness between altruists and beneficiaries within these colonies. Population structure was described using hierarchical F-statistics and an identity by descent measure, developed by Queller and Goodnight (1989), was used to estimate intracolony relatedness. It was found that inbreeding was not contributing to between-group genetic variance, at any level, in a consistent manner across localities. Therefore relatedness, considered in isolation, does not seem sufficient to account for the presence of worker behavior. It is suggested that large benefits for group living may be responsible for maintaining altruistic behavior, in part, in this species. Significant heterogeneity among localities for all F-statistics estimated in our analysis was found and this may be attributable to stochastic elements such as cofounding behavior and the low percentage of males in the brood. The possible consequences of such heterogeneity in population structure for the maintenance of altruism in E. bicolor are discussed.     

Genetic structure of an Apis dorsata population: the significance of migration and colony aggregation

Eight microsatellite loci were used to investigate the genetic structure of the giant honeybee (Apis dorsata) population in northeast India. This species migrates seasonally between summer and winter nesting sites, and queens appear to return to their previously occupied site. Furthermore, there is a strong tendency for colonies of this species to aggregate at perennially utilized nesting sites that may be shared by more than 150 colonies. These behavioral features suggest that colonies within aggregations should be more related than random colonies, but that the long-distance migration could act to minimize genetic differentiation both between geographical areas and within aggregations. Our genetic study supports these conjectures arising from natural history. A. dorsata aggregations are comprised of colonies that share more alleles than expected by chance. Although queens heading neighboring colonies are not close relatives, fixation indices show significant genetic differentiation among aggregation sites. However, there appears to be sufficient gene flow among aggregations to prevent high degrees of relatedness developing between colonies within aggregations. The results also suggest that there is significant population structuring between geographical regions, although the level of structuring caused by aggregation exceeds the differentiation attributable to geographic region.     

Fine-grained spatial genetic structure in the bivalve Gemma gemma from Maine and Virginia (USA), as revealed by Inter-Simple Sequence Repeat markers

Gemma gemma is a small ovoviviparous bivalve distributed in shallow sand flats along the North American Atlantic and Gulf of Mexico coasts. Genetic variation in G. gemma was analysed by means of Inter-Simple Sequence Repeats (ISSRs) at the following levels: (i) between localities (Maine and Virginia), (ii) among 10-m-diameter patches within localities, and (iii) within patches. Thirty individuals/patch and three patches/locality were analysed. Individuals were genotyped for 67 ISSR polymorphic loci from five primers. The portion of the genetic variation found between localities (2%) was small compared to that found either among patches within localities (37%) or within patches (61%). ISSRs in G. gemma allowed the detection of significant differentiation at individual and patch levels. By contrast, a low degree of genetic variability was found between localities. The small-scale genetic heterogeneity does not follow a simple, consistent pattern. Our results contrast with the generally accepted rule that aplanic species are locally homogeneous and globally heterogeneous and teleplanic species are the inverse.     

Range-wide population genetic structure of Symbiodinium associated with the Caribbean Sea fan coral, Gorgonia ventalina

Numerous marine invertebrates form endosymbiotic relationships with dinoflagellates of the genus Symbiodinium, yet few studies have examined the population structure of these symbionts. Here, we elucidate the population genetic structure of Symbiodinium harboured by the Caribbean octocoral Gorgonia ventalina throughout the entire range of the host. We used ten microsatellite loci to survey 35 localities spanning 3124 km across the Caribbean and Western Atlantic. Diversity of Symbiodinium haplotypes was low within colonies of G. ventalina but high among colonies. Despite high haplotypic diversity, significant evidence of clonal reproduction in Symbiodinium was detected, and most clones occurred within localities, not among them. Pairwise measures of F(ST) illustrated significant differentiation in 98% of comparisons between localities, suggesting low levels of gene flow. Clustering analyses identified six genetic groups whose distribution delimited four broad biogeographic regions. There was evidence of some connectivity among regions, corresponding with known geographic and oceanographic features. Fine-scale spatial surveys of G. ventalina colonies failed to detect differentiation among Symbiodinium at the metre scale. However, significant differentiation was observed among Symbiodinium hosted by sympatric G. ventalina colonies of different size/age classes. This cohort effect suggests that Symbiodinium may have an epidemic population structure, whereby G. ventalina recruits are infected by the locally predominant symbiont strain(s), which change over time.     

Social flexibility in a primitively social allodapine bee (Hymenoptera: Apidae): results of a translocation experiment

Many species of social animals are known to exhibit intraspecific variation in social traits between different populations. In the social insects, geographically separate populations may show wide-ranging forms of social behaviour, presumably because of variation in environmental parameters such as climate. For example, several bee species are known to exhibit eusocial or solitary behaviour depending on the latitude or altitude of the population. However, there is little or no empirical evidence to determine if this variation is a result of behavioural plasticity or long-term adaptation to local conditions, both of which have implications for the evolution of sociality. In this study, colonies of the allodapine bees Exoneura robusta and E. nigrescens were translocated between a montane and heathland habitat in southern Australia to assess the effect of habitat change on social behaviour. Results indicate that brood development in translocated colonies of both species differed from control colonies, leading to opportunities for different forms of social behaviour. However, there was also a high degree of variation within each habitat, suggesting an influence of both within and between habitat factors.     

Sex ratios, local fitness enhancement and eusociality in the allodapine bee Exoneura richardsoni

Previous studies of a facultatively eusocial allodapine bee, Exoneura richardsoni Rayment, indicated that high levels of cooperative nesting among close relatives seem to be maintained by benefits that lead to increases in per capita brood production. These traits could lead to local fitness enhancement, which in turn could select for female-biased sex ratios. We show here that sex investment ratios in this species are female-biased in small colony sizes, becoming progressively male-biased in larger colonies, consistent with expectations for local fitness enhancement, but not explainable by alternative models. Our results support previous suggestions that local fitness enhancement can lead to sex ratio bias in primitively social Hymenoptera, but differ from previous studies by suggesting that patterns of bias could lower selective thresholds for sib-directed altruism in small colonies, but have an opposing effect in large colonies.     

Limited direct effects of a massive wildfire on its sagebrush steppe bee community

1. Fire can affect bees directly through exposure to heat and smoke. Direct effects include mortality, injury, and displacement affecting at most two generations – adults and any immature progeny present during the fire. To study the direct effects of fire on bees, two criteria must be met. First, bees must be sampled soon after the fire event, before colonists arrive from outside the burn. Second, sampling locations must be far enough into the burned habitat to ensure that bees observed are survivors, and not foragers nesting outside the burn. 2. Bees were systematically sampled far inside (>7 km) and outside the burn perimeter immediately following a massive wildfire that burned primarily at night in sagebrush steppe habitat. Because adult females sleep in their nests, it was hypothesised that females of species with nests >10 cm underground would be safe from lethal heat, whereas females with shallow or above‐ground nests would be vulnerable. It was also hypothesised that fire would kill proportionately more males, as they typically sleep above ground. 3. Adult bees were present at all burned sample sites 14 and 21 days after the fire started. Many females were observed transporting pollen, indicative of active nest provisioning. Among the guild of bees surveyed at wild sunflowers (the only surviving flowering plant), fewer species were active within the burn. Guild composition was significantly altered, particularly by loss or depletion of several (but not all) sunflower specialists. Sex ratios did not shift, possibly due to surviving males aggregating in remaining patches of sunflowers.     

Do common eiders nest in kin groups? Microgeographic genetic structure in a philopatric sea duck

We investigated local genetic associations among female Pacific common eiders (Somateria mollissima v‐nigrum) nesting in a stochastic Arctic environment within two groups of barrier islands (Simpson Lagoon and Mikkelsen Bay) in the Beaufort Sea, Alaska. Nonrandom genetic associations were observed among nesting females using regional spatial autocorrelation analyses for distance classes up to 1000 m in Simpson Lagoon. Nearest‐neighbour analyses identified clusters of genetically related females with positive lr values observed for 0–13% and 0–7% of the comparisons in Simpson Lagoon and Mikkelsen Bay, respectively, across years. These results indicate that a proportion of females are nesting in close proximity to more genetically related individuals, albeit at low frequency. Such kin groupings may form through active association between relatives or through natal philopatry and breeding site fidelity. Eiders nest in close association with driftwood, which is redistributed annually by seasonal storms. Yet, genetic associations were still observed. Microgeographic structure may thus be more attributable to kin association than natal philopatry and site fidelity. However, habitat availability may also influence the level of structure observed. Regional structure was present only within Simpson Lagoon and this island group includes at least three islands with sufficient driftwood for colonies, whereas only one island at Mikkelsen Bay has these features. A long‐term demographic study is needed to understand more fully the mechanisms that lead to fine‐scale genetic structure observed in common eiders breeding in the Beaufort Sea.     

Strong constraints to independent nesting in a facultatively social bee: quantifying the effects of enemies-at-the-nest

Constraints to independent nesting play a key role in the understanding of social evolution in insects, but the source and the magnitude of such constraints are poorly known for many key taxa. In allodapine bees it is known that solitary nesting females have low rates of successful brood rearing and that this drives selection for cooperative nesting. It has been hypothesized that these constraints are due to the presence of enemies-at-the-nest, such as ants, but no direct link has been demonstrated between such enemies and colony failure. We set up an experiment in which solitary founded nests of an Australian allodapine bee, Exoneura nigrescens, were either protected from non-flying predators or left unprotected, and compared the resulting colony survival and brood production rates. We found that protected colonies have much higher rates of survival and that the constraints to independent nesting are extreme, with a mean of less than one offspring per nest at the end of the brood rearing period. This means that cooperative nesting is essential for this species to persist in its habitat. Received 6 July 2007; revised 5 November 2007; accepted 12 November 2007.     

Microhabitat use by wild-ranging Cabrera voles <Emphasis Type="Italic">Microtus cabrerae</Emphasis> as revealed by live trapping

The conservation problems affecting the endangered rodent Microtus cabrerae are mainly related to habitat loss and fragmentation. In the present study, we examined the presence/absence of the species in a group of potentially suitable habitat patches, and then evaluated the microhabitat attributes of locations used by wild-ranging individuals within occupied patches. Our results revealed that shallow flooding and abundant grass cover appear to be important factors in determining the presence among localities, but high rush cover strongly determined the presence and habitat use by voles both among and within localities. The preservation of these microhabitat characteristics may be required to effectively ensure the occurrence and stability of M. cabrerae colonies.     

Nest Suitability,Fine-Scale Population Structure and Male-Mediated Dispersal of a Solitary Ground Nesting Bee in an Urban Landscape

Bees are the primary pollinators of flowering plants in almost all ecosystems. Worldwide declines in bee populations have raised awareness about the importance of their ecological role in maintaining ecosystem functioning. The naturally strong philopatric behavior that some bee species show can be detrimental to population viability through increased probability of inbreeding. Furthermore, bee populations found in human-altered landscapes, such as urban areas, can experience lower levels of gene flow and effective population sizes, increasing potential for inbreeding depression in wild bee populations. In this study, we investigated the fine-scale population structure of the solitary bee Colletes inaequalis in an urbanized landscape. First, we developed a predictive spatial model to detect suitable nesting habitat for this ground nesting bee and to inform our field search for nests. We genotyped 18 microsatellites in 548 female individuals collected from nest aggregations throughout the study area. Genetic relatedness estimates revealed that genetic similarity among individuals was slightly greater within nest aggregations than among randomly chosen individuals. However, genetic structure among nest aggregations was low (Nei’s G_ST = 0.011). Reconstruction of parental genotypes revealed greater genetic relatedness among females than among males within nest aggregations, suggesting male-mediated dispersal as a potentially important mechanism of population connectivity and inbreeding avoidance. Size of nesting patch was positively correlated with effective population size, but not with other estimators of genetic diversity. We detected a positive trend between geographic distance and genetic differentiation between nest aggregations. Our landscape genetic models suggest that increased urbanization is likely associated with higher levels of inbreeding. Overall, these findings emphasize the importance of density and distribution of suitable nesting patches for enhancing bee population abundance and connectivity in human dominated habitats and highlights the critical contribution of landscape genetic studies for enhanced conservation and management of native pollinators.     

Gene flow on the ice: genetic differentiation among Adélie penguin colonies around Antarctica

Each summer Adélie penguins breed in large disjunct colonies on ice-free areas around the Antarctic continent. Comprising > 10 million birds, this species represents a dominant feature of the Antarctic ecosystem. The patchy distribution within a large geographical range, natal philopatry and a probable history of refugia, suggest that this species is likely to exhibit significant genetic differentiation within and among colonies. We present data from seven microsatellite DNA loci for 442 individuals from 13 locations around the Antarctic continent. With the exception of one locus, there was no significant genic or genotypic heterogeneity across populations. Pairwise FST values were low with no value > 0.02. When all colonies were compared in a single analysis, the overall FST value was 0.0007. Moreover, assignment tests were relatively ineffective at correctly placing individuals into their respective collection sites. These data reveal a lack of genetic differentiation between Adélie penguin colonies around the Antarctic continent, despite substantial levels of genetic variation. We consider this homogeneity in terms of the dispersal of individuals among colonies and the size of breeding groups and discuss our results in terms of the glacial history of Antarctica.     

Ecological Disturbance Through Patch-Burn Grazing Influences Lesser Prairie-Chicken Space Use

Across portions of the western Great Plains in North America, natural fire has been removed from grassland ecosystems, decreasing vegetation heterogeneity and allowing woody encroachment. The loss of fire has implications for grassland species requiring diverse vegetation patches and structure or patches that have limited occurrence in the absence of fire. The lesser prairie-chicken (Tympanuchus pallidicinctus) is a declining species of prairie-grouse that requires heterogeneous grasslands throughout its life history and fire has been removed from much of its occupied range. Patch-burn grazing is a management strategy that re-establishes the fire-grazing interaction to a grassland system, increasing heterogeneity in vegetation structure and composition. We evaluated the effects of patch-burn grazing on lesser prairie-chicken space use, habitat features, and vegetation selection during a 4-year field study from 2014–2017. Female lesser prairie-chickens selected 1- and 2-year post-fire patches during the lekking season, ≥4-year post-fire patches during the nesting season, and year-of-fire and 1-year post-fire patches during post-nesting and nonbreeding seasons. Vegetation selection during the lekking season was not similar to available vegetation in selected patches, suggesting that lesser prairie-chickens cue in on other factors during the lekking season. During the nesting season, females selected nest sites with greater visual obstruction, which was available in ≥4-year post-fire patches; during the post-nesting season, females selected sites with 15–25% bare ground, which was available in the year-of-fire, 1-year post-fire, and 2-year post-fire patches; and during the nonbreeding season they selected sites with lower visual obstruction, available in the year-of-fire and 1-year post-fire patches. Because lesser prairie-chickens selected all available time-since-fire patches during their life history, patch-burn grazing may be a viable management tool to restore and maintain lesser prairie-chicken habitat on the landscape. © 2021 The Wildlife Society.     

Breed Locally,Disperse Globally: Fine-Scale Genetic Structure Despite Landscape-Scale Panmixia in a Fire-Specialist

An exciting advance in the understanding of metapopulation dynamics has been the investigation of how populations respond to ephemeral patches that go ‘extinct’ during the lifetime of an individual. Previous research has shown that this scenario leads to genetic homogenization across large spatial scales. However, little is known about fine-scale genetic structuring or how this changes over time in ephemeral patches. We predicted that species that specialize on ephemeral habitats will delay dispersal to exploit natal habitat patches while resources are plentiful and thus display fine-scale structure. To investigate this idea, we evaluated the effect of frequent colonization of ephemeral habitats on the fine-scale genetic structure of a fire specialist, the black-backed woodpecker (Picoides arcticus) and found a pattern of fine-scale genetic structure. We then tested for differences in spatial structure between sexes and detected a pattern consistent with male-biased dispersal. We also detected a temporal increase in relatedness among individuals within newly burned forest patches. Our results indicate that specialist species that outlive their ephemeral patches can accrue significant fine-scale spatial structure that does not necessarily affect spatial structure at larger scales. This highlights the importance of both spatial and temporal scale considerations in both sampling and data interpretation of molecular genetic results.     

Consistent spatial scaling of high-severity wildfire can inform expected future patterns of burn severity

Increasing wildfire activity in forests worldwide has driven urgency in understanding current and future fire regimes. Spatial patterns of area burned at high severity strongly shape forest resilience and constitute a key dimension of fire regimes, yet remain difficult to predict. To characterize the range of burn severity patterns expected within contemporary fire regimes, we quantified scaling relationships relating fire size to patterns of burn severity. Using 1615 fires occurring across the Northwest United States between 1985 and 2020, we evaluated scaling relationships within fire regimes and tested whether relationships vary across space and time. Patterns of high-severity fire demonstrate consistent scaling behaviour; as fire size increases, high-severity patches consistently increase in size and homogeneity. Scaling relationships did not differ substantially across space or time at the scales considered here, suggesting that as fire-size distributions potentially shift, stationarity in patch-size scaling can be used to infer future patterns of burn severity.     

Evaluating food availability and nest predation risk as sources of bias in aural bird surveys

ABSTRACT The use of aural surveys to estimate population parameters is widespread in avian studies. Despite efforts to increase the efficacy of this method, the potential for ecological context to bias population estimates remains largely unexplored. For example, food availability and nest predation risk can influence singing activity independent of density and, therefore, may bias aural estimates where these ecological factors vary systematically among habitats or other categories of ecological interest. We used a natural fire event in a mixed‐conifer forest that experienced variation in fire severity (low, intermediate, and high) to determine if aural surveys produce accurate density estimates of Dark‐eyed Juncos ( Junco hyemalis) independent of ecological context. During the first 2‐yr postfire, we censused junco populations in each burn type with intensive spot‐mapping and nest searching, locating 168 nests. Simultaneously, we conducted fixed‐radius point‐count surveys and estimated food availability and nest predation risk in each burn type to test whether ecological context may influence aural detection probability independent of actual density. We found no difference in nesting densities among patches burned at different severity. Arthropod food availability was inversely related to fire severity during the first postfire breeding season, but increased to higher levels across all severities during the second. In both years, aural detections were significantly greater in intermediate severity patches that consistently represented the habitat with the lowest nest predation risk. These results suggest that nest predation risk may significantly bias aural estimates of avian populations. Although traditional aural survey methods such as the Breeding Bird Survey measure habitat attributes, our findings highlight the difficulty in assessing relevant covariates in estimates of avian population. Future research must consider the potential for nest predation and other ecological factors to drive interannual or interhabitat variation in avian population estimates independent of true changes in population size.     

Genetic variation,multiple paternity,and measures of reproductive success in the critically endangered hawksbill turtle (Eretmochelys imbricata)

The Yucatán Peninsula in Mexico contains some of the largest breeding groups of the globally distributed and critically endangered hawksbill turtle (Eretmochelys imbricata). An improved understanding of the breeding system of this species and how its genetic variation is structured among nesting areas is required before the threats to its survival can be properly evaluated. Here, we genotype 1195 hatchlings and 41 nesting females at 12 microsatellite loci to assess levels of multiple paternity, genetic variation and whether individual levels of homozygosity are associated with reproductive success. Of the 50 clutches analyzed, only 6% have multiple paternity. The distribution of pairwise relatedness among nesting localities (rookeries) was not random with elevated within‐rookery relatedness, and declining relatedness with geographic distance indicating some natal philopatry. Although there was no strong evidence that particular rookeries had lost allelic variation via drift, younger turtles had significantly lower levels of genetic variation than older turtles, suggesting some loss of genetic variation. At present there is no indication that levels of genetic variation are associated with measures of reproductive success such as clutch size, hatching success, and frequency of infertile eggs.     

White-Headed Woodpecker Nesting Ecology After Wildfire

ABSTRACT Within forests susceptible to wildfire and insect infestations, land managers need to balance dead tree removal and habitat requirements for wildlife species associated with snags. We used Mahalanobis distance methods to develop predictive models of white-headed woodpecker (Picoides albolarvatus) nesting habitat in postfire ponderosa pine (Pinus ponderosa)-dominated landscapes on the Fremont-Winema National Forests in south central Oregon, USA. The 1-km radius (314 ha) surrounding 45 nest sites was open-canopied before fire and a mosaic of burn severities after wildfire. The 1-ha surrounding nests of white-headed woodpeckers had fewer live trees per hectare and more decayed and larger diameter snags than at non-nest sites. The leading cause of nest failure seemed to be predation. Habitat and abiotic features were not associated with nest survival. High daily survival rates and little variation within habitat features among nest locations suggest white-headed woodpeckers were consistently selecting high suitability habitats. Management activities that open the forest canopy and create conditions conducive to a mosaic burn pattern will probably provide suitable white-headed woodpecker nesting habitat after wildfire. When making postfire salvage logging decisions, we suggest that retention of larger, more decayed snags will provide nesting habitat in recently burned forests.     

HOW SEDENTARY ARE GREYWING FRANCOLINS (FRANCOLINUS AFRICANUS)?

Phasianids are considered to be sedentary birds with limited dispersal so that populations may be expected to show genetic isolation by distance. To test this, we examined genetic variability in 618 greywing francolins (Francolinus africanus) at 24 localities over a 1,500 km² area. We subdivided the samples to measure genetic population structure among localities separated by 6–60 km, and among coveys separated by 0.1–6 km. Thirteen of 30 (43%) allozyme loci were polymorphic, and heterozygosity ranged from 5.3 to 8.5% over 24 localities and averaged 7.0%, a value much larger than that found for other phasianids. Significant allele-frequency heterogeneity was detected among localities and among coveys at several localities for several loci. Mantel's test, however, showed that there was no correlation between geographical distance and the allele-frequency difference between localities for all but one allele. Although spatial autocorrelation was detected with Moran's I and Geary's c for two alleles, the geographical patterns of I in correlograms of 18 independent alleles showed a “crazy-quilt” pattern of allele-frequency patches. This shows that the isolation-by-distance model of subpopulation structure is inappropriate for these birds. Individuals, therefore, appear to disperse far beyond neighboring populations. “Private-allele” and F_ST estimates of migration under the island model were 8–9 individuals between localities of each generation. Allele-frequency heterogeneity, large amounts of gene flow, and the general lack of spatial autocorrelation imply that the small, socially-structured populations of greywing are subject to high rates of turnover, founder effects, and random drift.     

Habitat Use and Selection by California Spotted Owls in a Postfire Landscape

ABSTRACT Forest fire is often considered a primary threat to California spotted owls (Strix occidentalis occidentalis) because fire has the potential to rapidly alter owl habitat. We examined effects of fire on 7 radiomarked California spotted owls from 4 territories by quantifying use of habitat for nesting, roosting, and foraging according to severity of burn in and near a 610-km²fire in the southern Sierra Nevada, California, USA, 4 years after fire. Three nests were located in mixed-conifer forests, 2 in areas of moderate-severity burn, and one in an area of low-severity burn, and one nest was located in an unburned area of mixed-conifer-hardwood forest. For roosting during the breeding season, spotted owls selected low-severity burned forest and avoided moderate- and high-severity burned areas; unburned forest was used in proportion with availability. Within 1 km of the center of their foraging areas, spotted owls selected all severities of burned forest and avoided unburned forest. Beyond 1.5 km, there were no discernable differences in use patterns among burn severities. Most owls foraged in high-severity burned forest more than in all other burn categories; high-severity burned forests had greater basal area of snags and higher shrub and herbaceous cover, parameters thought to be associated with increased abundance or accessibility of prey. We recommend that burned forests within 1.5 km of nests or roosts of California spotted owls not be salvage-logged until long-term effects of fire on spotted owls and their prey are understood more fully.