Neural mechanisms involved in female mate choice in invertebrates

Mate choice is a critical decision with direct implications for fitness. Although it has been recognized for over 150 years, our understanding of its underlying mechanisms is still limited. Most studies on mate choice focus on the evolutionary causes of behavior, with less attention given to the physiological and molecular mechanisms involved. This is especially true for invertebrates, where research on mate choice has largely focused on male behavior. This review summarizes the current state of knowledge on the neural, molecular and neurohormonal mechanisms of female choice in invertebrates, including behaviors before, during, and after copulation. We identify areas of research that have not been extensively explored in invertebrates, suggesting potential directions for future investigation. We hope that this review will stimulate further research in this area.

Behavioral convergence in defense behaviors in pair bonded individuals correlates with neuroendocrine receptors in the medial amygdala

Monogamous, pair-bonded animals coordinate intra-pair behavior for spatially separated challenges including territorial defense and nest attendance. Paired California mice, a monogamous, territorial and biparental species, approach intruders together or separately, but often express behavioral convergence across intruder challenges. To gain a more systems-wide perspective of potential mechanisms contributing to behavioral convergence across two conspecific intruder challenges, we conducted an exploratory study correlating behavior and receptor mRNA (Days 10 and 17 post-pairing). We examined associations between convergence variability in pair time for intruder-oriented behaviors with a pair mRNA index for oxytocin (OXTR), androgen (AR), and estrogen alpha (ERα) receptors within the medial amygdala (MeA) and the anterior olfactory nucleus (AON), brain regions associated with social behavior. An intruder behavior index revealed a bimodal distribution of intruder-related behaviors in Challenge 1 and a unimodal distribution in Challenge 2, suggesting population behavioral convergence, but no significant correlations with neuroendocrine measures. However, OXTR, AR, and ERα mRNA in the MeA were positively associated with convergence in individual intruder-related behaviors, suggesting multiple mechanisms may influence convergence. Mice could also occupy the nest during intruder challenges and convergence in nest attendance was positively correlated with MeA OXTR. At an individual level, nest attendance was positively associated with MeA ERα. Vocalizations were positively associated with AR and ERα mRNA. No positive associations were found in the AON. Overall, neuroendocrine receptors were implicated in convergence of a monogamous pair's defense behavior, highlighting the potential importance of the MeA as part of a circuit underlying convergence.

The acoustic response of snapping shrimp to synthetic impulsive acoustic stimuli between 50 and 600 Hz

There is growing concern that the noise from human activities in water may impact the detection and production of sound by aquatic animals. Snapping shrimp are sound producing crustaceans and their sound has biological and ecological importance. This paper investigated the effects of pulsed stimuli upon the acoustic behavior of these animals. Changes in snap frequency and duration were assessed before, during and after playbacks and at different levels. Acoustic analysis showed that the duration of the snaps increased significantly during playbacks, whereas the snap peak frequency significantly decreased compared to before and after exposure. Data also showed that when exposed to a sound pressure level equal and above to 130 re 1 μPa (computed particle motion 2.06 × 10^-06 m/s), shrimp responded acoustically. The results suggested that the pulsed acoustic stimuli triggered a behavioral response that included more snapping from bigger animals and movements away from the source.

Snapping shrimp have helmets that protect their brains by dampening shock waves

Shock waves are supersonic high-amplitude pressure waves that cause barotrauma when they transfer kinetic energy to the tissues of animals.^1-4 Snapping shrimp (Alpheidae) produce shock waves and are exposed to them frequently, so we asked if these animals have evolved mechanisms of physical protection against them. Snapping shrimp generate shock waves by closing their snapping claws rapidly enough to form cavitation bubbles that release energy as an audible "snap" and a shock wave when they collapse.^5-8 We tested if snapping shrimp are protected from shock waves by a helmet-like extension of their exoskeleton termed the orbital hood. Using behavioral trials, we found shock wave exposure slowed shelter-seeking and caused a loss of motor control in Alpheus heterochaelis from which we had removed orbital hoods but did not significantly affect behavior in shrimp with unaltered orbital hoods. Shock waves thus have the potential to harm snapping shrimp but may not do so under natural conditions because of protection provided to shrimp by their orbital hoods. Using pressure recordings, we discovered the orbital hoods of A. heterochaelis dampen shock waves. Sealing the anterior openings of orbital hoods diminished how much they altered the magnitudes of shock waves, which suggests these helmet-like structures dampen shock waves by trapping and expelling water so that kinetic energy is redirected and released away from the heads of shrimp. Our results indicate orbital hoods mitigate blast-induced neurotrauma in snapping shrimp by dampening shock waves, making them the first biological armor system known to have such a function.

Testosterone pulses paired with a location induce a place preference to the nest of a monogamous mouse under field conditions

Changing social environments such as the birth of young or aggressive encounters present a need to adjust behavior. Previous research examined how long-term changes in steroid hormones mediate these adjustments. We tested the novel concept that the rewarding effects of transient testosterone pulses (T-pulses) in males after social encounters alters their spatial distribution on a territory. In free-living monogamous California mice (Peromyscus californicus), males administered three T-injections at the nest spent more time at the nest than males treated with placebo injections. This mimics T-induced place preferences in the laboratory. Female mates of T-treated males spent less time at the nest but the pair produced more vocalizations and call types than controls. Traditionally, transient T-changes were thought to have transient behavioral effects. Our work demonstrates that in the wild, when T-pulses occur in a salient context such as a territory, the behavioral effects last days after T-levels return to baseline.

Sound pressure and particle motion components of the snaps produced by two snapping shrimp species (Alpheus heterochaelis and Alpheus angulosus)

Snapping shrimps are pervasive generators of underwater sound in temperate and tropical coastal seas across oceans of the world. Shrimp snaps can act as signals to conspecifics and provide acoustic information to other species and even to humans for habitat monitoring. Despite this, there are few controlled measurements of the acoustic parameters of these abundant acoustic stimuli. Here, the characteristics of snaps produced by 35 individuals of two species, Alpheus heterochaelis and Alpheus angulosus, are examined to evaluate the variability within and between the species. Animals were collected from the wild and the sound pressure and particle acceleration were measured at 0.2, 0.5, and 1 m from individual shrimp in controlled laboratory conditions to address the snap properties at communication-relevant distances. The source and sound exposure levels (at 1 m) were not significantly different between these two species. The frequency spectra were broadband with peak frequencies consistently below 10 kHz. The particle acceleration, the sound component likely detectable by shrimp, was measured across three axes. The directional amplitude variation suggests that the particle motion of snaps could act as a localization cue. The amplitudes of the snap pressure and acceleration decreased with distance, yet the levels remained sufficient for the predicted detection range by nearby conspecifics.

Influence of reproductive output on divorce rates in polar seabirds

The high occurrence of social monogamy in birds has led to questions about partner fidelity, or the perennial nature of monogamy from one breeding season to another. Despite the evolutionary advantages of partner fidelity, divorce occurs among 95% of bird species. We aimed to describe patterns of divorce and partner fidelity in five seabird species breeding in Arctic and Antarctic regions and investigated the influence of breeding status on pair bond maintenance. For four out of the five species considered, we observed low divorce rates (respectively 1.9%, 3.3%, 2.5%, and 0.0% for Brünnich's guillemot, glaucous gull, Antarctic petrel, and south polar skua), while the divorce rate was much higher (19.1%) for the black-legged kittiwake. For kittiwakes, the divorce rate was lower for pairs that managed to raise their chick to 15 days of age, while the effect of breeding success on divorce in the four other species could not be tested due to the rareness of divorce events. Our results emphasize the potentially large temporal (interannual) variations that should be taken into account in understanding divorce and partner fidelity in seabirds.

Pair-bonding leads to convergence in approach behavior to conspecific vocalizations in California mice (Peromyscus californicus)

Pair-bonding allows for division of labor across behavioral tasks such as protecting a territory, caring for pups or foraging for food. However, how these labor divisions are determined, whether they are simply intrinsic differences in the individual's behavior or a coordinated behavioral response by the pair, remains unknown. We used the monogamous, biparental and territorial California mouse (Peromyscus californicus) to study how behavioral approach to an aggressive vocal stimulus in a novel environment was affected by pair-bonding. Using a three-chambered vocal playback paradigm, we first measured the amount of time individuals spent in close proximity to aggressive bark vocalizations. We found that animals could be categorized as either approachers or avoiders. We then paired individuals based on their initial approach behavior to an opposite sex individual who displayed either similar or different approach behaviors. These pairs were then retested for approach behavior as a dyad 10-11 days post-pairing. This test found that pairs showed convergence in their behavioral responses, such that pairs who were mismatched in their approach behaviors became more similar, and pairs that were matched remained so. Finally, we analyzed the ultrasonic vocalizations (USV) produced and found that pairs produced significantly more USVs than individuals. Importantly, increased USV production correlated with increasing behavioral convergence of pairs. Taken together, this study shows that pair-bonded animals alter their approach behaviors to coordinate their response with their partner and that vocal communication may play a role in coordinating these behavioral responses. Overall, our findings indicate that pair-bonding generates an emergent property in pairs, adjusting their combined approach behavior towards a new aggressive stimulus representing a potential challenge to the bonded pair. Such findings may be broadly important for social bonding in other social systems.

Mating System of the Snapping Shrimp Synalpheus brevicarpus (Caridea, Alpheidae) Inhabiting Sponges Dysidea sp. (Demospongiae)

AbstractThe lifestyle of symbiotic species in the genus Synalpheus can vary from pair living to eusocial. A pair-living social system commonly implies the adoption of a monogamous mating system. In this study, we used the symbiotic shrimp Synalpheus brevicarpus in association with the sponge Dysidea sp. to test the hypothesis that heterosexual pairs of symbiotic shrimps can adopt a monogamous mating system when living in association with a morphologically complex host. We collected a total of 40 sponges, which were inhabited by 76 shrimps: 41 males, 33 females, and 2 juveniles. Synalpheus brevicarpus is sexually dimorphic, with males displaying proportionately larger weaponry (snapping claws) and a smaller average body size than females. Sponges were more often inhabited by a pair of heterosexual shrimps than expected by chance. Larger sponges were inhabited by more than one pair of shrimps in which the sex ratio did not differ significantly from 1∶1. Pairs of heterosexual shrimps were recorded, with females carrying embryos in all stages of embryonic development. Our results indicate that S. brevicarpus is a pair-living shrimp with a monogamous social and mating system that may also guard spaces or areas within its sponge host. Our hypothesis of monogamy is supported by the observations on pair living, sex ratio, and sexual dimorphism in body size and weaponry in this species.

Sexual and reproductive traits of the pearl oyster shrimp Pontonia margarita (Decapoda: Palemonidae), symbiotically inhabiting the mantle cavity of the rugose pen shell Pinna rugosa (Bivalvia: Pinnidae)

Symbiosis between decapods and mollusks provides a unique opportunity to examine some of the evolutionary strategies employed by marine invertebrates. We describe the sexual and reproductive traits of the pearl oyster shrimp, Pontoniamargarita Verril, 1869, found symbiotically inhabiting the mantle cavity of the rugose pen shell, Pinnarugosa Sowerby, 1835. Solitary males and females (ovigerous and non-ovigerous) and heterosexual pairs (with ovigerous and non-ovigerous females) were found in a total of 47 rugose pen shells collected from a sandy area with seagrass meadows on the southeastern coast of the Gulf of California, Mexico. The body length (BL) of female P.margarita was correlated with the shell volume of their rugose pen shell host. The sex ratio was female-biased (0.85M:1F). Female P.margarita were larger than their male counterparts in terms of BL, cephalothorax length (CL), and the maximum chelae length of the second pereopod (MCL). The CL and MCL were more strongly correlated for males (r = 0.70, p = 0.01). The number and volume of eggs per ovigerous female varied from 95 to 1,571 and from 5.46 ± 0.48 to 8.85 ± 0.97 mm3, respectively. Our results indicate polygamous behavior and social monogamy among P.margarita, and a short-term pairing system for their association with P.rugosa.

It takes two: Seasonal variation in sexually dimorphic weaponry results from divergent changes in males and females

Sexually dimorphic weaponry often results from intrasexual selection, and weapon size can vary seasonally when costs of bearing the weapon exceed the benefits outside of the reproductive season. Weapons can also be favored in competition over nonreproductive resources such as food or shelter, and if such nonreproductive competition occurs year-round, weapons may be less likely to vary seasonally. In snapping shrimp (Alpheus angulosus), both sexes have an enlarged snapping claw (a potentially deadly weapon), and males of many species have larger claws than females, although females are more aggressive. This contrasting sexual dimorphism (larger weaponry in males, higher aggression in females) raises the question of whether weaponry and aggression are favored by the same mechanisms in males and females. We used field data to determine whether either sex shows seasonal variation in claw size such as described above. We found sexual dimorphism increased during the reproductive season due to opposing changes in both male and female claw size. Males had larger claws during the reproductive season than during the nonreproductive season, a pattern consistent with sexual selection. Females, however, had larger claws during the nonreproductive season than during the reproductive season-a previously unknown pattern of variation in weapon size. The observed changes in female weapon size suggest a trade-off between claw growth and reproduction in the reproductive season, with investment in claw growth primarily in the nonreproductive season. Sexually dimorphic weaponry in snapping shrimp, then, varies seasonally due to sex differences in seasonal patterns of investment in claw growth, suggesting claws may be advantageous for both sexes but in different contexts. Thus, understanding sexual dimorphisms through the lens of one sex yields an incomplete understanding of the factors favoring their evolution.

When to Cheat: Modeling Dynamics of Paternity and Promiscuity in Socially Monogamous Prairie Voles (Microtus ochrogaster)

In many socially monogamous species, individuals form long-term pair bonds and males mate guard females. Such behavior is thought to help secure intra-pair fertilizations, the result of intra-pair copulations (IPCs), and ensure paternity. However, socially monogamous males are also often opportunistic and seek additional mating opportunities with other females, leaving their partner unguarded. The success associated with a male’s decision to seek more mates over guarding his partner might be impacted by the activity of other males, specifically the proportion of other males leaving their territories to seek extra-pair copulations (EPCs). The amount of EPC-seeking males can impact the likelihood of a given male encountering an unguarded paired female, but also of being cuckolded (losing IPCs). It remains unclear under which conditions it is optimal to stay and guard or seek EPCs. Using field data from socially monogamous prairie voles (Microtus ochrogaster) to generate parameters, we used optimal performance modeling (Monte Carlo simulations) to ask when is it most reproductively advantageous for a bonded male to seek EPCs, despite the risk of losing IPCs. We defined three types of males: exclusive mating bonded males (true residents), non-exclusive mating bonded residents (roving residents), and unpaired males (wanderers). We first modeled the success of an individual male living in a context that incorporated only true and roving residents. We next added wandering males to this model. Finally, we considered the effects of including wandering males and unpaired females in our model. For all contexts, we found that as EPC-seeking in the population increases, the potential reproductive benefit for seeking EPCs increasingly outpaces the rate of cuckolding. In other words, we observe a shift in optimal strategy from true residents to rovers among paired males. Our models also demonstrate that reproductive fitness is likely to remain constant, despite the shift toward obtaining success via EPCs over IPCs. Our results show the dynamic nature of reproductive decision-making, and demonstrate that alternative reproductive decisions yield subtle but important differences despite appearing as balanced strategies.

Pair bond endurance promotes cooperative food defense and inhibits conflict in coral reef butterflyfish

Pair bonding is generally linked to monogamous mating systems, where the reproductive benefits of extended mate guarding and/or of bi-parental care are considered key adaptive functions. However, in some species, including coral reef butterflyfishes (f. Chaetodonitidae), pair bonding occurs in sexually immature and homosexual partners, and in the absence of parental care, suggesting there must be non-reproductive adaptive benefits of pair bonding. Here, we examined whether pair bonding butterflyfishes cooperate in defense of food, conferring direct benefits to one or both partners. We found that pairs of Chaetodon lunulatus and C. baronessa use contrasting cooperative strategies. In C. lunulatus, both partners mutually defend their territory, while in C. baronessa, males prioritize territory defence; conferring improvements in feeding and energy reserves in both sexes relative to solitary counterparts. We further demonstrate that partner fidelity contributes to this function by showing that re-pairing invokes intra-pair conflict and inhibits cooperatively-derived feeding benefits, and that partner endurance is required for these costs to abate. Overall, our results suggest that in butterflyfishes, pair bonding enhances cooperative defense of prey resources, ultimately benefiting both partners by improving food resource acquisition and energy reserves.

Sound production patterns of big-clawed snapping shrimp (Alpheus spp.) are influenced by time-of-day and social context

Snapping shrimp are perhaps the most pervasive sources of biological sound in the ocean. The snapping sounds of cryptic shrimp colonies in shallow coastal habitats worldwide create a near-continuous crackling with high spatiotemporal variability, yet the underlying acoustic ecology is not well understood. This study investigated sound production rates and acoustic behavior of snapping shrimp species common in the Western Atlantic Ocean and Gulf of Mexico (Alpheus heterochaelis and Alpheus angulosus). Snap rates were measured in a controlled laboratory setting under natural light, temperature, and substrate conditions for shrimp held individually, in pairs, and in a ten-shrimp mesocosm, to test hypotheses that acoustic activity varies with time-of-day and social context. Spontaneous snapping was observed for 81 out of 84 solitary shrimp monitored. Time-of-day influenced snap output for individuals and same-sex pairs-higher rates occurred during dusk and night, compared to daylight hours, but this pattern was inconsistent for opposite-sex pairs and a mixed-sex group. These laboratory results provide insight into behavioral rhythms that may influence snapping patterns in natural populations, and underscore the limited understanding of a major sound source in marine environments.

Socio-ecological features other than sex affect habitat selection in the socially obligate monogamous Eurasian beaver

Habitat selection is a context-dependent mechanism, in which both the internal state as well as external factors affect the behavior and decisions of an individual. This is well known for polygamous mammals, which are typically sexually dimorphic, and often express great variability in behavior and habitat selection between individuals as well between the sexes. Among monogamous mammals, however, variability in habitat selection should be explained by group characteristics and the presence of offspring rather than by sex. We evaluated this hypothesis in a socially monogamous rodent, the Eurasian beaver (Castor fiber), in a saturated Norwegian population. For the first time in this species we applied GPS tracking devices (N = 22 adult beavers, in 15 territories, 2009–2013), and used resource selection functions (i) to document population-wide habitat selection and the importance of ‘territory’ therein, and (ii) to evaluate which socio-ecological factors explained potential individual differences in habitat selection. We found that variation in habitat selection was stronger between territories than between years or individuals nested by territory. We identified that family size and the presence of kits, but not sex, explained individual variation in habitat selection. Adults with kits and/or larger families tended to exhibit low risk-taking behavior (avoiding human-related variables such as roads, buildings, and agricultural land), and stayed close to their main lodge (parental care). Our results show that habitat selection is a context-dependent mechanism even in a species which expresses very little behavioral and morphological dimorphism.

Inferences on mating and sexual systems of two Pacific Cinetorhynchus shrimps (Decapoda, Rhynchocinetidae) based on sexual dimorphism in body size and cheliped weaponry

Sexual dimorphism in body size and weaponry was examined in two Cinetorhynchus shrimp species in order to formulate hypotheses on their sexual and mating systems. Collections of Cinetorhynchus sp. A and Cinetorhynchus sp. B were made in March, 2011 on Coconut Island, Hawaii, by hand dipnetting and minnow traps in coral rubble bottom in shallow water. Although there is overlap in male and female size, some males are much larger than females. The major (pereopod 1) chelipeds of males are significantly larger and longer than those of females. In these two Cinetorhynchus species, males and females have third maxillipeds of similar relative size, i.e., those of males are not hypertrophied and probably not used as spear-like weapons as in some other rhynchocinetid (Rhynchocinetes) species. Major chelae of males vary with size, changing from typical female-like chelae tipped with black corneous stout setae to subchelate or prehensile appendages in larger males. Puncture wounds or regenerating major chelipeds were observed in 26.1 % of males examined (N = 38 including both species). We interpret this evidence on sexual dimorphism as an indication of a temporary male mate guarding or "neighborhoods of dominance" mating system, in which larger dominant robustus males defend females and have greater mating success than smaller males. Fecundity of females increased with female size, as in most caridean species (500-800 in Cinetorhynchus sp. A; 300-3800 in Cinetorhynchus sp. B). Based on the sample examined, we conclude that these two species have a gonochoric sexual system (separate sexes) like most but not all other rhynchocinetid species in which the sexual system has been investigated.

Schistosome monogamy: who, how, and why?

Schistosomes represent a unique animal model for comparative analyses of monogamy. Indeed, schistosomes are classified at the lowest taxonomical level of monogamous species and lack complex social interactions, which could alter our understanding of their unusual mating system. Elements discussed here include the fact that monogamy in schistosomes could be an ancestral state between hermaphroditism and polygyny or polygynandry and the occurrence of mate changes. In addition, hypotheses are proposed to explain monogamy in schistosomes (e.g. female dispersion, the need for paternal care, oviposition site limitation or aggressiveness, and mate guarding). We also propose future experimental and analytical approaches to improve our understanding of the schistosomes' mating system.

Monogamy in an Australian arboreal marsupial, the yellow-bellied glider (Petaurus australis)

Several Australian arboreal marsupials have been reported to show variation in mating system across populations, but most previous studies have not included genetic analyses to confirm the observations. Our aim was to test the hypothesis that monogamy was the predominant mating system in a population of yellow-bellied gliders (Petaurus australis) in south-western Victoria, using a combination of behavioural observations and molecular genetic analyses. Home-range overlap, cohesiveness of pairs, rates of den site co-occupancy and location of den trees within the home ranges of 13 adult gliders were determined via radio-tracking. A monogamous social system predominated, demonstrated by extensive home-range overlap between cohabiting adult males and females (40–100%) and little home-range overlap between adjacent territories (<14%). Males spent ~55% of their active time within 25 m of their female partners and 55–85% of their sleeping time in dens with their female partner. The parentage of all juveniles spotlighted within the 400-ha study area was analysed using five microsatellite DNA markers. Of 37 individuals genotyped, eight of 13 juveniles were assigned both social parents as true parents with ≥80% confidence. These results suggest that social and genetic monogamy predominated in this population of yellow-bellied gliders.

Cryptic biodiversity and phylogeographical patterns in a snapping shrimp species complex

Recent investigations suggest that marine biodiversity may be much higher than earlier estimates, and an important hidden source of diversity in marine systems is the phenomenon of cryptic species complexes. Such complexes are informative models for research into the evolutionary processes that govern species compositions of marine fauna. The snapping shrimp genera Alpheus and Synalpheus are known to harbour large numbers of cryptic species; here, I characterize the genetic structure of the Alpheus armillatus species complex in the northern Caribbean, west Atlantic, and Gulf of Mexico using mitochondrial and nuclear sequence data. Over this geographical region, the complex harbours at least three lineages that are probable reproductively isolated species; all major lineages diverged subsequent to the close of the Isthmus of Panama. Only one lineage was present in the Gulf of Mexico, whereas outside the Gulf of Mexico there was no clear tendency for lineage dominance by geographical region, as most sites were populated by shrimp from at least two lineages. However, within each lineage, there was strong evidence of population genetic differentiation between geographical regions. All lineages showed strong signals of demographic expansion, and one lineage showed sharply reduced genetic diversity, suggestive of past population bottlenecks or recently founded populations with low gene flow from other sites. These results show that evolutionary processes leading to divergence and speciation have been common and recent in the snapping shrimp, and suggest that connectivity among shrimp populations may be limited.

Sexual Dimorphism in Territorial Scent Marking by Adult Eurasian Beavers (Castor fiber)

Mammalian scent marking is often associated with territorial defense. However, males and females may demonstrate different activity patterns and play different roles. Female mammals nurture the young during lactation, while males purportedly perform other tasks more frequently, such as territorial maintenance and defense. This paper investigates the contribution made by mated pairs of adult males and females to territorial scent-marking in the obligate monogamous Eurasian beavers (Castor fiber). We hypothesized that both sexes should show territorial behavior, and predicted that they deposit a higher proportion of scent marks at borders. We also hypothesized that a sexual dimorphism exists due to reproductive constraints on the females, and predicted that males should invest significantly more in scent-marking behavior than females during summer. We obtained behavioral data by radio tracking six mated pairs of Eurasian beavers during spring and summer 2000-2001 on two rivers in southeastern Norway. Our results showed that both males and females clustered their scent marks near territorial borders, but males deposited a larger number of scent marks than females and spent more time at borders. Males were also found to have a higher scent marking rate and scent marks per night than females during summer, but not during spring. Overall, scent marks per night were higher in males than females. We conclude that both males and females Eurasian beavers carry out territorial behavior by scent marking, but males carry a larger part of the territorial defense during summer when females lactate. Our results are discussed in the light of the codefense hypothesis.

Complex mating system and dispersal patterns in a social lizard, Egernia whitii

In contrast to the polygynous mating systems typically displayed by most reptilian taxa, long-term genetic monogamy appears to be widespread within a lineage of group-living Australian scincid lizards, the Egernia group. We have recently shown that White's skink, Egernia whitii, lives in small but temporally stable social aggregations. Here, we examine the mating system, spatial organization, and dispersal patterns of E. whitii using behavioural field studies and data from four microsatellite loci. Parentage analysis of E. whitii litters revealed that its mating system is characterized by both polygyny and monogamy. Polygyny was the predominant mating system but within-season social and genetic monogamy was common (36-45% of breeding pairs). The incidence of between-season monogamy in E. whitii was rare compared to that reported for its congeners. Low levels of multiple paternity (12% of litters) and extra-group paternity (16%) were detected. Social groups are generally comprised of closely related individuals, but breeding pairs were not more closely related compared to other potential mates. Spatial autocorrelation analyses revealed significant positive local genetic structure over 50 m, which was consistent for all age-sex classes. There was no clear and consistent evidence for sex-biased dispersal, with assignment tests (mean assignment index) and relatedness analyses suggesting female-biased dispersal, but spatial autocorrelation analyses indicating a trend for male-biased dispersal. We discuss the implication of our results in regard to the factors promoting the evolution of monogamy within the Egernia group.

Genetic, ecological, and behavioural divergence between two sibling snapping shrimp species (Crustacea: Decapoda: Alpheus)

Examination of genetic and ecological relationships within sibling species complexes can provide insights into species diversity and speciation processes. Alpheus angulatus and A. armillatus, two snapping shrimp species with overlapping ranges in the north-western Atlantic, are similar in morphology, exploit similar ecological niches and appear to represent recently diverged sibling species. We examined phylogenetic and ecological relationships between these two species with: (i) sequence data from two mitochondrial genes (16S rRNA and COI); (ii) data on potential differences in microhabitat distribution for A. armillatus and A. angulatus; and (iii) data from laboratory experiments on the level of reproductive isolation between the two species. DNA sequence data suggest A. armillatus and A. angulatus are sister species that diverged subsequent to the close of the Isthmus of Panama, and that haplotype diversity is lower in A. armillatus than in A. angulatus. Both species are distantly related to A. heterochaelis and A. estuariensis, two species with which A. angulatus shares some similarities in coloration. Ecological data on the distribution of A. angulatus and A. armillatus from two locations revealed differences in distribution of the two species between habitat patches, with each patch dominated by one or the other species. However, there was no apparent difference in distribution of the two species within habitat patches with respect to microhabitat location. Ecological data also revealed that heterospecific individuals often occur in close proximity (i.e. within metres or centimetres) where sympatric. Behavioural data indicated that these species are reproductively isolated, which is consistent with speciation in transient allopatry followed by post-divergence secondary contact. Our data further resolve taxonomic confusion between the sibling species, A. armillatus and A. angulatus, and suggest that sympatry in areas of range overlap and exploitation of similar ecological niches by these two recently diverged species have selected for high levels of behavioural incompatibility.