Similar Life History Research Articles

Analysis of Genetic Diversity and Population Structure in Sophora japonica Linn. in China With Newly Developed SSR Markers

Sophora japonica is a medium-sized deciduous native tree to China. Its flower buds and fruits have special medicinal value. By using 26 highly variable nuclear microsatellites, newly reported here, we assessed the genetic diversity and population structure of 10 representative populations (180 individuals in total) within the species. The results revealed a relatively high genetic diversity in S. japonica (Na = 8.00, He = 0.74, PIC = 0.80, I = 1.67), and reduced genetic variation and heterozygote excess were detected in landrace populations (Na = 5.59, He = 0.71, Ar = 4.11, FIS = − 0.043) when compared with those semi-wild population (Na = 9.7, He = 0.74, Ar = 8.80, FIS = 0.082). A significant bottleneck was detected in two Landraces populations. Moderate differentiation and frequent gene flow were detected among all populations (FST = 0.079, P < 0.05, Nm = 2.893). Mantel test detected a marginal significant pattern of isolation by distance (r = 0.009, P = 0.50), and strong differentiation was observed between most southern and northern populations both by the STRUCTURE clustering and principal coordinate analysis (PCoA), indicating that geographic isolation played a key role in the genetic differentiation of the species. The results from this study will benefit the breeding and conservation of S. japonica, other congener species, and tree species with similar life history traits.

Stability of native and exotic lady beetle populations in a diverse landscape

AbstractThe stability of populations is a central, yet challenging concept in ecology. Here, we examine the stability of annual abundance for populations of nine native and four exotic lady beetle species (Coccinellidae) in a mixed landscape in Michigan, USA, over 23 yr. The species have similar life histories, live together in the same habitats, and have been disturbed by the sequential introduction of exotic lady beetle species. The publicly available dataset was collected in a diverse landscape of three forest habitats, four annual crop habitats with different intensities of management, and three perennial crops. Replicated 1‐ha plots were sampled weekly with yellow sticky cards during the summer season for each habitat, three plots for each of the three forest types and six plots for each of the seven crop habitats. We quantified stability for each species and each species by habitat combination, using three parameters: trends in abundance, persistence, and temporal population variability. The most abundant lady beetle species were more stable than the uncommon and rare species. Habitat generalists had more stable population dynamics than specialists, but habitat breadth was confounded with lady beetle abundance. Exotic and native species with similar abundances had similar levels of stability. Exotic species disrupted the native populations, leading to declines in abundance for eight of nine species and increased population variability for the native species. The abundances of exotic lady beetles rose quickly to the long‐term mean. Our findings support the hypothesis that populations exhibit species‐specific levels of stability, not greatly affected by stochastic variations in environmental conditions or by habitat characteristics. We also show that exotic species can decrease the stability as well as the abundance of native species in a community of lady beetles.

Males have more aggressive and less sociable personalities than females in semi-captive Asian elephants

Personality, i.e. consistent between-individual differences in behaviour, has been documented in many species. Yet little is known about how males and females of long-lived, highly social species differ in their measures of personality structure. We investigated sex differences in the mean, variance, and covariance of three previously reported personality traits (Attentiveness, Sociability, Aggressiveness) in 150 female and 107 male Asian elephants (Elephas maximus) from a semi-captive population in Myanmar. These three personality traits were obtained by performing exploratory factor analysis on 28 behavioural items that had been rated by experienced elephant handlers. We found that males scored significantly higher on Aggressiveness and tended to score lower on Sociability than females. However, no sex difference was found in the mean scores of Attentiveness. Variances for the three personality traits did not differ between the sexes, suggesting that male and female elephants share the same range of personality variation. Likewise, trait covariances were similar between the sexes. While both sexes show complex sociality in the wild, female Asian elephants typically live in highly social family units, whereas male elephants’ social bonds are weaker. Males usually form dominance ranks by aggressive interactions, especially during musth. Our results on a large sample of individuals living in their natural environment are thus in agreement with elephant life-histories and parallel the findings of sex differences in other long-lived highly social species with similar life-histories.

The complete mitogenome of the springtail Tullbergia bisetosa: a subterranean springtail from the sub-Antarctic region

Tullbergia bisetosa is a springtail (Collembola) native to the sub-Antarctic Prince Edward Islands. Unlike most other springtails, it has acquired a euedaphic (living within the soil) life form. In the present study, the complete mitogenome of T. bisetosa was sequenced. It has a length of 15,204 bp and comprises 13 protein-coding genes, 22 tRNAs, and two rRNAs. The mitogenome has the following base composition: A = 35.5%, T = 32.3%, G = 10.6%, and C = 21.1%. A Bayesian phylogenetic tree shows that T. bisetosa is grouped with springtails that possess similar morphological features and similar life histories. Our results suggest a mitogenomic signal towards morphological traits that conforms to a euedaphic lifestyle.

High sensitivity of a keystone forage fish to elevated CO2 and temperature.

Sand lances of the genus Ammodytes are keystone forage fish in coastal ecosystems across the northern hemisphere. Because they directly support populations of higher trophic organisms such as whales, seabirds or tuna, the current lack of empirical data and, therefore, understanding about the climate sensitivity of sand lances represent a serious knowledge gap. Sand lances could be particularly susceptible to ocean warming and acidification because, in contrast to other tested fish species, they reproduce during boreal winter months, and their offspring develop slowly under relatively low and stable pCO2 conditions. Over the course of 2 years, we conducted factorial pCO2 × temperature exposure experiments on offspring of the northern sand lance Ammodytes dubius, a key forage species on the northwest Atlantic shelf. Wild, spawning-ripe adults were collected from Stellwagen Bank National Marine Sanctuary (Cape Cod, USA), and fertilized embryos were reared at three pCO2 conditions (400, 1000 and 2100 μatm) crossed with three temperatures (5, 7 and 10 ˚C). Exposure to future pCO2 conditions consistently resulted in severely reduced embryo survival. Sensitivity to elevated pCO2 was highest at 10 ˚C, resulting in up to an 89% reduction in hatching success between control and predicted end-of-century pCO2 conditions. Moreover, elevated pCO2 conditions delayed hatching, reduced remaining endogenous energy reserves at hatch and reduced embryonic growth. Our results suggest that the northern sand lance is exceptionally CO2-sensitive compared to other fish species. Whether other sand lance species with similar life history characteristics are equally CO2-sensitive is currently unknown. But the possibility is a conservation concern, because many boreal shelf ecosystems rely on sand lances and might therefore be more vulnerable to climate change than currently recognized. Our findings indicate that life history, spawning habitat, phenology and developmental rates mediate the divergent early life CO2 sensitivities among fish species.

Distribution and Genetic Diversity of the Rare Plant Veratrum woodii (Liliales: Melanthiaceae) in Georgia: A Preliminary Study with AFLP Fingerprint Data

Veratrum woodii, a long-lived herbaceous perennial species, has a fragmented distribution with populations scattered in the southeastern and lower midwestern USA. In Georgia, the species has a protection status of rare. This preliminary study focused on verifying historic and/or unvouchered populations in Georgia and characterizing variation and genetic structure within and among all populations in the state. We analyzed AFLP (amplified fragment length polymorphism) data as dominantly inherited markers for 16 populations sampled from Georgia, Florida, and Missouri. Our results suggest that this species overall has relatively low levels of genetic diversity and that differentiation among populations is comparable to species with similar life history traits. Measures of genetic diversity, such as mean He, indicate that variation of populations has some partitioning between disjunct northern and southern Georgia (and Florida) populations. However, our analyses imply that watershed assignment, rather than geographic distance, provides a better explanation for variation and population structure. We hypothesize that southern relict populations in Georgia may have served as refugia during Pleistocene glaciations. We conclude that life-history characteristics, low levels of genetic variation, and suppression of ecological disturbance collectively jeopardize populations of Veratrum woodii in Georgia.

Contrasting population genetic structure in three aggregating groupers (Percoidei: Epinephelidae) in the Indo-West Pacific: the importance of reproductive mode

BackgroundUnderstanding the factors shaping population genetic structure is important for evolutionary considerations as well as for management and conservation. While studies have revealed the importance of palaeogeographic changes in shaping phylogeographic patterns in multiple marine fauna, the role of reproductive behaviour is rarely considered in reef fishes. We investigated the population genetics of three commercially important aggregating grouper species in the Indo-West Pacific, namely the camouflage grouper Epinephelus polyphekadion, the squaretail coral grouper Plectropomus areolatus, and the common coral trout P. leopardus, with similar life histories but distinct spatio-temporal characteristics in their patterns of forming spawning aggregations.ResultsBy examining their mitochondrial control region and 9–11 microsatellite markers, we found an overarching influence of palaeogeographic events in the population structure of all species, with genetic breaks largely coinciding with major biogeographic barriers. The divergence time of major lineages in these species coincide with the Pleistocene glaciations. Higher connectivity is evident in E. polyphekadion and P. areolatus that assemble in larger numbers at fewer spawning aggregations and in distinctive offshore locations than in P. leopardus which has multiple small, shelf platform aggregations.ConclusionsWhile palaeogeographic events played an important role in shaping the population structure of the target species, the disparity in population connectivity detected may be partly attributable to differences in their reproductive behaviour, highlighting the need for more investigations on this characteristic and the need to consider reproductive mode in studies of connectivity and population genetics.

Isolation and characterization of a temperature-sensitive lethal strain of Anopheles arabiensis for SIT-based application

BackgroundMalaria is still a global health problem and vector control is the cornerstone of disease control strategies using indoor residual insecticide spraying (IRS) and insecticide-treated nets. The situation is becoming acute with widespread resistance to the limited arsenal of available insecticide classes. Therefore, new and innovative tools to reduce Plasmodium transmission are in need and this situation raised considerable interest in using sterile insect technique (SIT) against human pest insects, particularly Anopheles malaria vectors. When considering a mosquito release programme, one of the first issues to be addressed is how to eliminate/separate the hematophagous vector females. In this paper, we report the development and evaluation of an Anopheles arabiensis temperature-sensitive lethal (tsl) strain towards its potential use for the development of a genetic sexing strain (GSS).Anopheles arabiensis male mosquitoes originated from North Cameroon were treated with 0.05% ethyl methanesulfonate (EMS). The mutagen was added to 10% sucrose solution and mosquitoes fed ad-libitum for 24h and 48h on a cotton wool soaked with sucrose-mutagen solution placed at the top of the cup. Treated males were then allowed to mate with wild virgin females and their progenies were screened for heat sensitivity from F3 to F8, until the isolation and establishment of a tsl strain which was further characterized by assessing its productivity (fecundity and fertility), larval development, adult longevity as well as nature and inheritance pattern of the tsl.ResultsObservations showed that the number of eggs laid and their hatch rate were similar between females that mated with mutagenized males and those from the control suggesting that mutagenesis didn't affect An. arabiensis male fecundity and fertility. At F3, fourteen isofemale families out of 88 tested, which showed mortalities ranged between 50 and 80 %, were selected as lines potentially containing a tsl mutation. From F4 to F8, a tsl strain was isolated and established by screening L1 larvae at 41°C for 3 hours. This strain showed similar life history traits compared to the wild type strain in terms of fertility, larval development time and adult's emergence. Crossing experiments to further assess the nature and inheritance pattern of the tsl phenotype showed that it is due to a recessive allele located on an autosome.ConclusionThe successful establishment of the An. arabiensis tsl strain is a valuable tool towards the development of a GSS for SIT applications against this species. This will be done by induction of a Y-autosome translocation to link the wild-type allele to the Y chromosome in such manner that males are wild-type (temperature resistant) and females are mutant (temperature sensitive).

Outlier SNPs detect weak regional structure against a background of genetic homogeneity in the Eastern Rock Lobster, Sagmariasus verreauxi

Genetic differentiation is characteristically weak in marine species making assessments of population connectivity and structure difficult. However, the advent of genomic methods has increased genetic resolution, enabling studies to detect weak, but significant population differentiation within marine species. With an increasing number of studies employing high resolution genome-wide techniques, we are realising that the connectivity of marine populations is often complex and quantifying this complexity can provide an understanding of the processes shaping marine species genetic structure and to inform long-term, sustainable management strategies. This study aims to assess the genetic structure, connectivity, and local adaptation of the Eastern Rock Lobster (Sagmariasus verreauxi), which has a maximum pelagic larval duration of 12 months and inhabits both subtropical and temperate environments. We used 645 neutral and 15 outlier SNPs to genotype lobsters collected from the only two known breeding populations and a third episodic population—encompassing S. verreauxi’s known range. Through examination of the neutral SNP panel, we detected genetic homogeneity across the three regions, which extended across the Tasman Sea encompassing both Australian and New Zealand populations. We discuss differences in neutral genetic signature of S. verreauxi and a closely related, co-distributed rock lobster, Jasus edwardsii, determining a regional pattern of genetic disparity between the species, which have largely similar life histories. Examination of the outlier SNP panel detected weak genetic differentiation between the three regions. Outlier SNPs showed promise in assigning individuals to their sampling origin and may prove useful as a management tool for species exhibiting genetic homogeneity.

Cranial shape parallelism in soft-furred sengis: moving on a geographic gradient

Sengis are small mammals in the order Macroscelidae that are shrew-like in appearance. They are cursorial and saltatorial, and both insectivorous and omnivorous. We studied Macroscelides spp. and Elephantulus rupestris with overlapping distributions in South Africa and Namibia. They have similar life histories and are good candidate species for comparative studies. We used geometric morphometric techniques for 3 views of a total of 43 skulls representing E. rupestris, M. flavicaudatus, and M. proboscideus to evaluate variation in skull shape that may be associated with geographical location. We pooled all Macroscelides into a single group because the speciation event was recent. We observed a pattern of shape variation in both taxa that followed a latitudinal gradient from the Western Province of Africa with Mediterranean vegetation to northern Namibia with xeric habitats. At higher latitudes, skulls were elongated with narrow frontals, premaxilla, and maxilla, while at low latitudes, the parietals were reduced and both occipitals and bullae timpanicae were expanded. We interpreted these patterns in the context of predator avoidance and foraging.

Pleistocene climate cycling and host plant association shaped the demographic history of the bark beetle Pityogenes chalcographus

Historical climatic oscillations and co-evolutionary dependencies were key evolutionary drivers shaping the current population structure of numerous organisms. Here, we present a genome-wide study on the biogeography of the bark beetle Pityogenes chalcographus, a common and widespread insect in Eurasia. Using Restriction Associated DNA Sequencing, we studied the population structure of this beetle across a wide part of its western Palaearctic range with the goal of elucidating the role of Pleistocene glacial-interglacial cycling and its close relationship to its main host plant Norway spruce. Genetic distance among geographic sites was generally low, but clustering analysis revealed three genetically distinct groups, that is, southern, central/south-eastern, and north-eastern locations. Thus, three key P. chalcographus glacial refugia were identified: in the Italian-Dinaric region, the Carpathians, and the Russian plain, shared with its main host. The current phylogeographic signal was affected by genetic divergence among geographically isolated refugia during glacial periods and postglacial re-establishment of genetic exchange through secondary contact, reflected by admixture among genetic groups. Additionally, certain life history traits, like the beetle’s dispersal and reproductive behaviour, considerably influenced its demographic history. Our results will help to understand the biogeography of other scolytine beetles, especially species with similar life history traits.

Life cycles and seasonal vertical distributions of copepods in the Iceland Sea

The sub-Arctic Iceland Sea is an important feeding area for the Icelandic capelin stock with copepods as a major food item. Information on the life history of copepods in the area is limited, and therefore the major aim of the present paper is to describe the population development and ontogenetic vertical migrations of dominant copepods in the area. Depth stratified samples were collected on six cruises covering all seasons of the year from 2006 to 2008. Calanus hyperboreus dominated the biomass (~ 45% of copepods), with C. finmarchicus ranking second (~ 28%) and Metridia longa third (~ 17%). The copepods differed in their life history strategies. C. hyperboreus is unique in that it has the deepest winter distribution (~ 800–1000 m), reproduces at depth in February–March in the absence of phytoplankton food, and spends relatively short time in the surface layers during summer. C. finmarchicus also hibernates at depth, however much shallower (~ 200-600 m), and the reproduction at the surface in May–June is timed to the productive period of phytoplankton. A 2- to 3-year life cycle is proposed for C. hyperboreus and a 1 year for C. finmarchicus. Pseudocalanus spp. appear to have a similar life history as C. finmarchicus, while occupying intermediate depths (~ 400–1000 m) during the overwintering period. The life history of the omnivorous species M. longa appears relatively decoupled from the phytoplankton spring bloom. The same applies to the omnivorous species Oithona spp. and Oncaea spp. The information presented adds to the comparative description and understanding of copepods in sub-Arctic areas in general.

Offshore Prey Densities Facilitate Similar Life History and Behavioral Patterns in Two Distinct Aquatic Apex Predators, Northern Pike and Lake Trout

AbstractNorthern Pike Esox lucius are important aquatic apex predators in freshwater ecosystems across the Canadian Boreal Shield. Although Northern Pike have historically been described as nearshore ambush predators, larger individuals have been anecdotally observed foraging in offshore habitats. We used two province‐wide data sets from Ontario, Canada, to investigate the degree to which Northern Pike are generalist predators by examining the influence of offshore prey fish densities on their life histories. To better understand whether the life history patterns observed were unique to Northern Pike or representative of aquatic apex predators generally, we compared Northern Pike life history and catch results to those of the Lake Trout Salvelinus namaycush, a well‐known pelagic apex predator. We found that the asymptotic lengths of both Northern Pike and Lake Trout were positively related to Cisco Coregonus artedi CPUE. Furthermore, both Northern Pike and Lake Trout occupied offshore habitat more frequently in lakes with greater Cisco CPUEs. Northern Pike early growth and mortality rates were negatively related to Cisco CPUE but positively related to Yellow Perch Perca flavescens CPUE, suggesting that Northern Pike undergo ontogenetic shifts to foraging on Ciscoes later in life. Although the growth and mortality of these predators were related to prey availability, variation in the CPUEs of Northern Pike and Lake Trout was best explained by physical lake characteristics. Our study suggests that Northern Pike and Lake Trout respond similarly to Cisco CPUE across the Canadian Boreal Shield, consistent with research reported for other aquatic apex predators. Results of this work collectively suggest that generalist behavior and large‐bodied life history strategies of Northern Pike are facilitated by the availability of Ciscoes.

GENETIC DIAGNOSIS AND REPRODUCTIVE BIOLOGY OF INTRODUCED MYSTACOLEUCUS MARGINATUS IN THE TOBA LAKE, NORTH SUMATRA

After M. marginatus has been introduced to Toba Lake, North Sumatra, the status of M.marginatus stocks and their biological properties is unknown. In this study, we examine the genetic patterns of the M. marginatus in Toba Lake, North Sumatra Province. Employing the cytochrome c oxidase subunit I (COI) gene of the mtDNA, we profile the genetic variation within M. marginatus in Toba Lake. We also analyzed reproductive characteristic and commercial catches of M. marginatus. The result shown M. marginatus is a synonim for M. marginatus, in total, 1 polymorphic sites (represent singleton dimensions) was identified and phylogenetic reconstruction reveal low levels of genetic diversity with no clear pattern of haplotype-partitioning. Nucleotide diversity analysis infer the present of two lineages. The Ne value of M. marginatus (1,936 to 3,878), the population has not experienced population growth/expansion as expected and the total production of M. marginatus in Toba Lakeof the year for 2013 has ranged between 3,347.05 – 6,694.1 ton. M. marginatus in the Toba Lake share similar life history traits include maximum body size, longevity, age at maturity, and fecundity(the number of eggs produced). M. marginatus is categorized as the opportunistic strategy consisted of fishes with short generation time, low batch fecundity, and low investment per offspring. This lifehistory traits approach of M. marginatus are important for guide fisheries management for its sustainability. More over the information can be use as pilot data and apply it to data-poor species.

Dynamic Energy Budget theory predicts smaller energy reserves in thyasirid bivalves that harbour symbionts

Dynamic Energy Budget (DEB) theory describes the ecophysiology of individuals and distinguishes between the biomass of an organism that functions as an energy reserve and as a structure. DEB theory offers a robust framework to infer and contrast energy allocation patterns, even in data-poor species. We used this approach to compare two thyasirid bivalves that have scarce data: Thyasira cf. gouldi and Parathyasira sp., which co-occur in a seasonal environment, show similar life history features, and are both particulate feeders. However, T. cf. gouldi hosts chemosymbiotic bacteria that are digested as an additional resource, and how this mixotrophy affects the energy budget of these chemosymbiotic thyasirids is unknown. We used allometric and life history data to parameterize a DEB model for each species and found that symbiotic T. cf. gouldi has a smaller fraction of its biomass as an energy reserve relative to Parathyasira. A smaller energy reserve, in turn, implies reduced energy assimilation and mobilization fluxes, lower somatic maintenance costs and growth rate, and larger energy allocation to maturity and reproduction in symbiotic T. cf. gouldi. For a thyasirid inhabiting an environment with seasonal forcing, these life history traits may represent an evolutionary strategy where the symbionts function as a partial energy reserve. Our results elucidate a potential role of the chemosymbiotic bacteria in the ecophysiology of a bivalve host, and highlight how the symbiotic association is likely to alter the energy budget of a mixotrophic thyasirid.

Lifelong population connectivity between large rivers and their tributaries: A case study of shovelnose sturgeon from the Mississippi and Wisconsin rivers

AbstractFishes that depend on large‐river habitats have declined in many regions due to human alteration of both mainstems and tributaries. Conserving these species is often complicated by their dependence on long‐distance movements to complete their life cycle, but the location of key habitats is difficult to assess across multiple life history stages. Movement of large‐river fishes between mainstems and major tributaries is commonly observed, but the role of these exchanges at the population level is uncertain. We used shovelnose sturgeon (Scaphirhynchus platorynchus) as a case study for assessing the lifelong spatial ecology of large‐river fishes. Fin ray microchemistry data indicate that shovelnose sturgeon from the Mississippi and Wisconsin rivers represent a unified population that relies on connections among multiple large‐river habitats throughout life history. The tributary serves as an important spawning area, but fin ray chemistry data suggest larvae subsequently drift downstream to nursery habitats in the mainstem; an assertion that is supported by extensive field survey data. Our analyses underscore the lifelong importance of connections within river networks for maintaining viable populations of this, and likely other large‐river species that have been documented to use tributary habitats. These findings support a metapopulation perspective on species that depend on large‐river habitats, many of which are now highly altered and fragmented. For shovelnose sturgeon and species with similar life history, protecting or restoring linkages between mainstem rivers and their tributaries should be a conservation priority.

Insects with similar social complexity show convergent patterns of adaptive molecular evolution

Eusociality has independently evolved multiple times in the hymenoptera, but the patterns of adaptive molecular evolution underlying the evolution and elaboration of eusociality remain uncertain. Here, we performed a population genomics study of primitively eusocial Polistes (paper wasps), and compared their patterns of molecular evolution to two social bees; Bombus (bumblebees), and Apis (honey bees). This species triad allowed us to study molecular evolution across a gradient of social complexity (Polistes < Bombus < Apis) and compare species pairs that have similar (i.e. Polistes and Bombus) or different (i.e. Polistes and Apis) life histories, while controlling for phylogenetic distance. We found that regulatory genes have high levels of positive selection in Polistes; consistent with the prediction that adaptive changes in gene regulation are important during early stages of social evolution. Polistes and Bombus exhibit greater similarity in patterns of adaptive evolution including greater overlap of genes experiencing positive selection, and greater positive selection on queen-biased genes. Our findings suggest that either adaptive evolution of a few key genes underlie the evolution of simpler forms of eusociality, or that the initial stages of social evolution lead to selection on a few key traits orchestrated by orthologous genes and networks.

Using spatially‐explicit capture–recapture models to explain variation in seasonal density patterns of sympatric ursids

Understanding how environmental factors interact to determine the abundance and distribution of animals is a primary goal of ecology, and fundamental to the conservation of wildlife populations. Studies of these relationships, however, often assume static environmental conditions, and rarely consider effects of competition with ecologically similar species. In many parts of their shared ranges, grizzly bears Ursus arctos and American black bears U. americanus have nearly complete dietary overlap and share similar life history traits. We therefore tested the hypothesis that density patterns of both bear species would reflect seasonal variation in available resources, with areas of higher primary productivity supporting higher densities of both species. We also hypothesized that interspecific competition would influence seasonal density patterns. Specifically, we predicted that grizzly bear density would be locally reduced due to the ability of black bears to more efficiently exploit patchy food resources such as seasonally abundant fruits. To test our hypotheses, we used detections of 309 grizzly and 597 black bears from two independent genetic sampling methods in spatially‐explicit capture–recapture (SECR) models. Our results suggest grizzly bear density was lower in areas of high black bear density during spring and summer, although intraspecific densities were also important, particularly during the breeding season. Black bears had lower densities in areas of high grizzly bear density in spring; however, density of black bears in early and late summer was best explained by primary productivity. Our results are consistent with the hypothesis that smaller‐bodied, more abundant black bears may influence the density patterns of behaviorally‐dominant grizzly bears through exploitative competition. We also suggest that seasonal variation in resource availability be considered in efforts to relate environmental conditions to animal density.

Sociality does not drive the evolution of large brains in eusocial African mole-rats

The social brain hypothesis (SBH) posits that the demands imposed on individuals by living in cohesive social groups exert a selection pressure favouring the evolution of large brains and complex cognitive abilities. Using volumetry and the isotropic fractionator to determine the size of and numbers of neurons in specific brain regions, here we test this hypothesis in African mole-rats (Bathyergidae). These subterranean rodents exhibit a broad spectrum of social complexity, ranging from strictly solitary through to eusocial cooperative breeders, but feature similar ecologies and life history traits. We found no positive association between sociality and neuroanatomical correlates of information-processing capacity. Solitary species are larger, tend to have greater absolute brain size and have more neurons in the forebrain than social species. The neocortex ratio and neuronal counts correlate negatively with social group size. These results are clearly inconsistent with the SBH and show that the challenges coupled with sociality in this group of rodents do not require brain enlargement or fundamental reorganization. These findings suggest that group living or pair bonding per se does not select strongly for brain enlargement unless coupled with Machiavellian interactions affecting individual fitness.

Demographic causes of adult sex ratio variation and their consequences for parental cooperation

The adult sex ratio (ASR) is a fundamental concept in population biology, sexual selection, and social evolution. However, it remains unclear which demographic processes generate ASR variation and how biases in ASR in turn affect social behaviour. Here, we evaluate the demographic mechanisms shaping ASR and their potential consequences for parental cooperation using detailed survival, fecundity, and behavioural data on 6119 individuals from six wild shorebird populations exhibiting flexible parental strategies. We show that these closely related populations express strikingly different ASRs, despite having similar ecologies and life histories, and that ASR variation is largely driven by sex differences in the apparent survival of juveniles. Furthermore, families in populations with biased ASRs were predominantly tended by a single parent, suggesting that parental cooperation breaks down with unbalanced sex ratios. Taken together, our results indicate that sex biases emerging during early life have profound consequences for social behaviour.