Female choice based on male spatial ability and aggressiveness among meadow voles

Cell proliferation and cell death levels in the dentate gyrus correlate with home range size among adult male meadow voles

Neurogenesis occurs throughout adulthood within the dentate gyrus, and evidence indicates that these new neurons play a critical role in both spatial and social memory. However, a vast majority of past research on adult neurogenesis has involved experiments with captive mice and rats, making the generalizability of results to natural settings questionable. We assessed the connection between adult neurogenesis and memory by measuring the home range size of wild-caught, free-ranging meadow voles (Microtus pennsylvanicus). Adult male voles (n = 18) were captured, fitted with radio collars, and released back into their natural habitat, where each vole's home range was assessed using 40 radio-telemetry fixes over the course of 5 evenings. Voles were then recaptured, and brain tissue was collected. Cellular markers of cell proliferation (pHisH3, Ki67), neurogenesis (DCX), and pyknosis were labeled on histological sections and then quantified using either fluorescent or light microscopy. Voles with larger home ranges had significantly higher pHisH3+ cell densities within the granule cell layer and subgranular zone (GCL+SGZ) of the dentate gyrus and higher Ki67+ cell densities in the dorsal GCL+SGZ. Voles with larger ranges also had significantly higher pyknotic cell densities in the entire GCL+SGZ and in the dorsal GCL+SGZ. These results support the hypothesis that cell proliferation and cell death within the hippocampus are involved with spatial memory formation. However, a marker of neurogenesis (DCX+) was not correlated with range size, suggesting that there may be selective cellular turnover in the dentate gyrus when a vole is ranging through its environment.

Limbic progesterone receptors regulate spatial memory

Progesterone and its receptors (PRs) participate in mating and reproduction, but their role in spatial declarative memory is not understood. Male mice expressed PRs, predominately in excitatory neurons, in brain regions that support spatial memory, such as the hippocampus and entorhinal cortex (EC). Furthermore, segesterone, a specific PR agonist, activates neurons in both the EC and hippocampus. We assessed the contribution of PRs in promoting spatial and non-spatial cognitive learning in male mice by examining the performance of mice lacking this receptor (PRKO), in novel object recognition, object placement, Y-maze alternation, and Morris-Water Maze (MWM) tasks. In the recognition test, the PRKO mice preferred the familiar object over the novel object. A similar preference for the familiar object was also seen following the EC-specific deletion of PRs. PRKO mice were also unable to recognize the change in object position. We confirmed deficits in spatial memory of PRKO mice by testing them on the Y-maze forced alternation and MWM tasks; PR deletion affected animal's performance in both these tasks. In contrast to spatial tasks, PR removal did not alter the response to fear conditioning. These studies provide novel insights into the role of PRs in facilitating spatial, declarative memory in males, which may help with finding reproductive partners.

Do male meadow voles (Microtus pennsylvanicus) always prefer and signal to 'popular' females? The role of social information context

For males, the behaviour of rival conspecifics can provide vital information about finding reproductively available females, and which have high-quality phenotypes. While valuable, this information represents sperm competition risk and even the potential for rejection by females. Thus, males should show flexibility in signalling behaviours towards females based on social information acquired with emphasis on the context of that information. We examined male meadow vole scent-marking behaviours and preferences for females based on previously obtained social information across different contexts. Social information context resulted in increased scent marking depending on the social odour pairing. Males scent marked more near a female whose odour had associated with three older rivals than one younger rival. But males marked equally toward a female whose odour had associated with three younger rivals and a female whose odour had associated with one older rival. This demonstrates that social odours are not of all equal value and that males can distinguish differences. Males then use these differences to tailor their signalling towards potentially high-quality phenotype females thereby maximizing their reproductive opportunities.

Sexual differences in responses of meadow voles to environmental cues in the presence of mink odor

In rodents, defensive behaviors increase the chances of survival during a predator encounter. Observable rodent defensive behaviors have been shown to be influenced by the presence of predator odors and nearby environmental cues such as cover, odors from conspecifics and food availability. Our experiment tested whether a predator scent cue influenced refuge preference in meadow voles within a laboratory setting. We placed voles in an experimental apparatus with bedding soaked in mink scent versus olive oil as a control across from four tubes that either contained (a) a dark plastic covering, (b) opposite-sex conspecific odor, (c) a food pellet, or (d) an empty, unscented space. A three-way interaction of tube contents, subject sex, and the presence of mink or olive oil on the preference of meadow voles to spend time in each area of the experimental apparatus and their latency to enter each area of the apparatus revealed sex differences in the environmental preference of meadow voles facing the risk of predation. The environmental preference of female, but not male, meadow voles was altered by the presence of mink urine or olive oil. A similar trend was found in the latency of males and females to enter each area of the experimental apparatus. These differences suggest that each sex utilizes different methods to increase their fitness when experiencing a predation risk. The observed sex differences may be explained by the natural history of voles owing to the differences in territorial range and the dynamics of evasion of terrestrial predators.

Differences in resource acquisition, not allocation, mediate the relationship between behaviour and fitness: a systematic review and meta-analysis

Within populations, individuals often show repeatable variation in behaviour, called 'animal personality'. In the last few decades, numerous empirical studies have attempted to elucidate the mechanisms maintaining this variation, such as life-history trade-offs. Theory predicts that among-individual variation in behavioural traits could be maintained if traits that are positively associated with reproduction are simultaneously associated with decreased survival, such that different levels of behavioural expression lead to the same net fitness outcome. However, variation in resource acquisition may also be important in mediating the relationship between individual behaviour and fitness components (survival and reproduction). For example, if certain phenotypes (e.g. dominance or aggressiveness) are associated with higher resource acquisition, those individuals may have both higher reproduction and higher survival, relative to others in the population. When individuals differ in their ability to acquire resources, trade-offs are only expected to be observed at the within-individual level (i.e. for a given amount of resource, if an individual increases its allocation to reproduction, it comes at the cost of allocation to survival, and vice versa), while among individuals traits that are associated with increased survival may also be associated with increased reproduction. We performed a systematic review and meta-analysis, asking: (i) do among-individual differences in behaviour reflect among-individual differences in resource acquisition and/or allocation, and (ii) is the relationship between behaviour and fitness affected by the type of behaviour and the testing environment? Our meta-analysis consisted of 759 estimates from 193 studies. Our meta-analysis revealed a positive correlation between pairs of estimates using both survival and reproduction as fitness proxies. That is, for a given study, behaviours that were associated with increased reproduction were also associated with increased survival, suggesting that variation in behaviour at the among-individual level largely reflects differences among individuals in resource acquisition. Furthermore, we found the same positive correlation between pairs of estimates using both survival and reproduction as fitness proxies at the phenotypic level. This is significant because we also demonstrated that these phenotypic correlations primarily reflect within-individual correlations. Thus, even when accounting for among-individual differences in resource acquisition, we did not find evidence of trade-offs at the within-individual level. Overall, the relationship between behaviour and fitness proxies was not statistically different from zero at the among-individual, phenotypic, and within-individual levels; this relationship was not affected by behavioural category nor by the testing condition. Our meta-analysis highlights that variation in resource acquisition may be more important in driving the relationship between behaviour and fitness than previously thought, including at the within-individual level. We suggest that this may come about via heterogeneity in resource availability or age-related effects, with higher resource availability and/or age leading to state-dependent shifts in behaviour that simultaneously increase both survival and reproduction. We emphasize that future studies examining the mechanisms maintaining behavioural variation in populations should test the link between behavioural expression and resource acquisition - both within and among individuals. Such work will allow the field of animal personality to develop specific predictions regarding the mediating effect of resource acquisition on the fitness consequences of individual behaviour.

Mate Choice, Sex Roles and Sexual Cognition in Vertebrates: Mate Choice Turns Cognition or Cognition Turns Mate Choice?

The idea of “smart is sexy,” meaning superior cognition provides competitive benefits in mate choice and, therefore, evolutionary advantages in terms of reproductive fitness, is both exciting and captivating. Cognitively flexible individuals perceive and adapt more dynamically to (unpredictable) environmental changes. The sex roles that females and males adopt within their populations can vary greatly in response to the prevalent mating system. Based on how cognition determines these grossly divergent sex roles, different selection pressures could possibly shape the (progressive) evolution of cognitive abilities, suggesting the potential to induce sexual dimorphisms in superior cognitive abilities. Associations between an individual’s mating success, sexual traits and its cognitive abilities have been found consistently across vertebrate species and taxa, providing evidence that sexual selection may well shape the supporting cognitive prerequisites. Yet, while superior cognitive abilities provide benefits such as higher feeding success, improved antipredator behavior, or more favorable mate choice, they also claim costs such as higher energy levels and metabolic rates, which in turn may reduce fecundity, growth, or immune response. There is compelling evidence in a variety of vertebrate taxa that females appear to prefer skilled problem-solver males, i.e., they prefer those that appear to have better cognitive abilities. Consequently, cognition is also likely to have substantial effects on sexual selection processes. How the choosing sex assesses the cognitive abilities of potential mates has not been explored conclusively yet. Do cognitive skills guide an individual’s mate choice and does learning change an individual’s mate choice decisions? How and to which extent do individuals use their own cognitive skills to assess those of their conspecifics when choosing a mate? How does an individual’s role within a mating system influence the choice of the choosing sex in this context? Drawing on several examples from the vertebrate world, this review aims to elucidate various aspects associated with cognitive sex differences, the different roles of males and females in social and sexual interactions, and the potential influence of cognition on mate choice decisions. Finally, future perspectives aim to identify ways to answer the central question of how the triad of sex, cognition, and mate choice interacts.

Let's get wild: A review of free-ranging rat assays as context-enriched supplements to traditional laboratory models

More than 24,000 rodent studies are published annually, with the vast majority of these studies focused on genetically undiverse animals in highly-controlled laboratory settings. However, findings from the laboratory have become increasingly unreliable for predicting outcomes in field and clinical settings, leading to a perceived crisis in translational research. One cause of this disparity might be that most human societies, in contrast to laboratory rodents, are genetically diverse and live in super-enriched environments. Methods for importing wild rats into the laboratory, and also exporting laboratory-style chambers into natural environments are not well-known outside their respective disciplines. Therefore, we have reviewed the current status of supplements to the laboratory rodent assay. We progress logically from highly-controlled experiments with natural breeding colonies to purely naturalistic approaches with free-ranging rats. We then highlight a number of approaches that allow genetically-diverse wild rats to be utilized in context-enriched paradigms. While considering the benefits and shortcomings of each available approach, we detail protocols for random sampling, remote-sensing, and deployment of laboratory chambers in the field. As supplements to standardized laboratory trials, some of these assays could offer key insights to help unify outcomes between laboratory and field studies. However, we note several outstanding questions that must be addressed such as: the trade-off between control and context, possible reductions in sample size, ramifications for the 'standardization fallacy', and ethical dilemmas of working with wild animals. Given these challenges, further innovation will be required before supplemental assays can be made broadly-accessible and thus, transferrable across disciplines.

Size Selective Harvesting Does Not Result in Reproductive Isolation among Experimental Lines of Zebrafish, Danio rerio: Implications for Managing Harvest-Induced Evolution

Simple Summary

Mortality in fish populations is commonly size-selective. In fisheries, larger fish are preferentially caught while natural predators preferentially consume smaller fish. Removal of certain sized fish from populations and elevated fishing mortality constitute a selection pressure which may change life-history, behaviour and reduce adult body-size. Because behaviour and body-size are related and influence mating preferences and reproductive output, size-selective mortality may favour subpopulations that less readily mate with each other. Our aim is to test this possibility using three experimental lines of zebrafish (Danio rerio) generated in laboratory by removing large-sized, small-sized and random-sized fish for five generations. We tested mating preferences among males and females and tested if they spawned together. We found males and females of all subpopulations to reproduce among themselves. Females generally preferred large-sized males. Females of all lines spawned with males, and males of all lines fertilised eggs of females independent of the subpopulation origin. Our study shows that size-selective mortality typical of fisheries or in populations facing heavy predation does not result in evolution of reproductive barriers. Thus, when populations adapted to fishing pressure come in contact with populations unexposed to such pressures, interbreeding may happen thereby helping exploited populations recover from harvest-induced evolution.

Abstract

Size-selective mortality is common in fish stocks. Positive size-selection happens in fisheries where larger size classes are preferentially targeted while gape-limited natural predation may cause negative size-selection for smaller size classes. As body size and correlated behavioural traits are sexually selected, harvest-induced trait changes may promote prezygotic reproductive barriers among selection lines experiencing differential size-selective mortality. To investigate this, we used three experimental lines of zebrafish (Danio rerio) exposed to positive (large-harvested), negative (small-harvested) and random (control line) size-selective mortality for five generations. We tested prezygotic preferences through choice tests and spawning trials. In the preference tests without controlling for body size, we found that females of all lines preferred males of the generally larger small-harvested line. When the body size of stimulus fish was statistically controlled, this preference disappeared and a weak evidence of line-assortative preference emerged, but only among large-harvested line fish. In subsequent spawning trials, we did not find evidence for line-assortative reproductive allocation in any of the lines. Our study suggests that size-selection due to fisheries or natural predation does not result in reproductive isolation. Gene flow between wild-populations and populations adapted to size-selected mortality may happen during secondary contact which can speed up trait recovery.

Problem-solving males become more attractive to female budgerigars

Darwin proposed that mate choice might contribute to the evolution of cognitive abilities. An open question is whether observing the cognitive skills of an individual makes it more attractive as a mate. In this study, we demonstrated that initially less-preferred budgerigar males became preferred after females observed that these males, but not the initially preferred ones, were able to solve extractive foraging problems. This preference shift did not occur in control experiments in which females observed males with free access to food or in which females observed female demonstrators solving these extractive foraging problems. Our results suggest that direct observation of problem-solving skills increases male attractiveness and that this could contribute to the evolution of the cognitive abilities underlying such skills.

Predictability is attractive: Female preference for behaviourally consistent males but no preference for the level of male aggression in a bi-parental cichlid

Although personality traits can largely affect individual fitness we know little about the evolutionary forces generating and maintaining personality variation. Here, we investigated the hypothesis that personality variation in aggression is sexually selected in the monogamous, bi-parental cichlid Pelvicachromis pulcher. In this species, breeding pairs form territories and they aggressively defend their territory and offspring against con- and heterospecific intruders. In our mate choice study, we followed up two alternative hypotheses. We either expected females to show a directional preference for a high level and high consistency of aggression (potentially indicating mate choice for male parental quality). Alternatively, we expected females to choose males for (dis-)similarity in the level/consistency of aggression (potentially indicating mate choice for compatibility). Individual level and consistency of aggression were assessed for males and females using mirror tests. After eavesdropping on aggressive behaviour of two males (differing in level and consistency of aggression) females were then allowed to choose between the two males. Males, but not females, showed personality variation in aggression. Further, females generally preferred consistent over inconsistent males independent of their level of aggression. We did not detect a general preference for the level of male aggression. However, we found an above average preference for consistent high-aggression males; whereas female preference for inconsistent high-aggression did not deviate from random choice. Our results suggest behavioural consistency of aggression in male rainbow kribs is selected for via female mate choice. Further, our study underlines the importance of considering both the level and the consistency of a behavioural trait in studies of animal behaviour.

Spatial memory is as important as weapon and body size for territorial ownership in a lekking hummingbird

Advanced cognitive abilities have long been hypothesized to be important in mating. Yet, most work on sexual selection has focused on morphological traits and its relevance for cognitive evolution is poorly understood. We studied the spatial memory of lekking long-billed hermits (Phaethornis longirostris) and evaluated its role in lek territory ownership, the magnitude of its effect compared to phenotypic traits expected to influence sexual selection, and whether its variation is indicated in the structure of mating vocal signal. Spatial memory (the ability to recall the position of a rewarding feeder) was compared between “territorial” and “floater” males. Interestingly, although spatial memory and body size both positively affected the probability of lek territory ownership, our results suggest a stronger effect of spatial memory. Bill tip length (used as weapon in agonistic interactions) also showed a positive but smaller effect. Load lifting during vertical flight, a measure of physical performance relevant to agonistic interactions, had no effect on territory ownership. Finally, both body size and spatial memory were indicated in the structure of male song: body size negatively correlated with song lowest frequency, while spatial memory positively predicted song consistency. Together, our findings lend support for cognition as a sexual selection target.

Song learning and cognitive ability are not consistently related in a songbird

Learned aspects of song have been hypothesized to signal cognitive ability in songbirds. We tested this hypothesis in hand-reared song sparrows (Melospiza melodia) that were tutored with playback of adult songs during the critical period for song learning. The songs developed by the 19 male subjects were compared to the model songs to produce two measures of song learning: the proportion of notes copied from models and the average spectrogram cross-correlation between copied notes and model notes. Song repertoire size, which reflects song complexity, was also measured. At 1 year of age, subjects were given a battery of five cognitive tests that measured speed of learning in the context of a novel foraging task, color association, color reversal, detour-reaching, and spatial learning. Bivariate correlations between the three song measures and the five cognitive measures revealed no significant associations. As in other studies of avian cognition, different cognitive measures were for the most part not correlated with each other, and this result remained true when 22 hand-reared female song sparrows were added to the analysis. General linear mixed models controlling for effects of neophobia and nest of origin indicated that all three song measures were associated with better performance on color reversal and spatial learning but were associated with worse performance on novel foraging and detour-reaching. Overall, the results do not support the hypothesis that learned aspects of song signal cognitive ability.

Male foraging efficiency, but not male problem-solving performance, influences female mating preferences in zebra finches

Experimental evidence suggests that females would prefer males with better cognitive abilities as mates. However, little is known about the traits reflecting enhanced cognitive skills on which females might base their mate-choice decisions. In particular, it has been suggested that male foraging performance could be used as an indicator of cognitive capacity, but convincing evidence for this hypothesis is still lacking. In the present study, we investigated whether female zebra finches (Taeniopygia guttata) modify their mating preferences after having observed the performance of males on a problem-solving task. Specifically, we measured the females’ preferences between two males once before and once after an observation period, during which their initially preferred male was incapable of solving the task contrary to their initially less-preferred male. We also conducted a control treatment to test whether the shift in female preferences was attributable to differences between the two stimulus males in their foraging efficiency. Finally, we assessed each bird’s performance in a color associative task to check whether females can discriminate among males based on their learning speed. We found that females significantly increased their preference toward the most efficient male in both treatments. Yet, there was no difference between the two treatments and we found no evidence that females assess male cognitive ability indirectly via morphological traits. Thus, our results suggest that females would not use the males’ problem-solving performance as an indicator of general cognitive ability to gain indirect fitness benefits (i.e., good genes) but rather to assess their foraging efficiency and gain direct benefits.

Multiple behavioural, morphological and cognitive developmental changes arise from a single alteration to early life spatial environment, resulting in fitness consequences for released pheasants

Subtle variations in early rearing environment influence morphological, cognitive and behavioural processes that together impact on adult fitness. We manipulated habitat complexity experienced by young pheasants (Phasianus colchicus) in their first seven weeks, adding a third accessible dimension by placing elevated perches in their rearing pens mimicking natural variation in habitat complexity. This simple manipulation provoked an interrelated suite of morphological, cognitive and behavioural changes, culminating in decreased wild mortality of birds from complex habitats compared with controls. Three mechanisms contribute to this: Pheasants reared with perches had a morphology which could enable them to fly to the higher branches and cope with prolonged roosting. They had a higher propensity to roost off the ground at night in the wild. More generally, these birds had more accurate spatial memory. Consequently, birds were at a reduced risk of terrestrial predation. The fitness consequences of variation in early rearing on behavioural development are rarely studied in the wild but we show that this is necessary because the effects can be broad ranging and not simple, depending on a complex interplay of behavioural, cognitive and morphological elements, even when effects that the treatments provoke are relatively short term and plastic.

The time interval between sequential mating affects the response of male meadow voles to previous mates

Male meadow voles differed in their copulatory behaviour, mating and reproductive success, and odour preferences for successively encountered mates, when the interval between pairing with two females was 1 h, 1 day, 4 days, 7 days or 10 days. Male voles had shorter latencies to first ejaculation with female 2 than with female 1 when the interval was 1 h, which may be attributed to heightened sexual arousal in males for female 2. Males also had shorter copulatory bouts with female 2 than with female 1 when the intervals between pairings were 1 h and 1 day. Shorter copulation bouts may allow more mating opportunities for both sexes and encourage multiple mating. Male voles also preferred the scent marks of female 2 to those of female 1 when the interval between pairing was 7 or 10 days, suggesting that these females were treated as distinct entities.

Condition dependence, developmental plasticity, and cognition: implications for ecology and evolution

Across taxa, both neural growth and cognitive function show considerable developmental plasticity. Data from studies of decision making, learning, and discrimination demonstrate that early life conditions have an impact on subsequent neural growth, maintenance, and cognition, with important ecological and evolutionary implications. Here, we provide a synthesis of the evidence that spatial and vocal learning are condition dependent, addressing what is known about their physiological control and the functional explanations. Neural investment is predicted to be affected by environmental conditions, but the shape of the response should depend on the fitness benefits of the cognitive traits under control. From an evolutionary perspective, traits promoting resistance to environmental perturbations should be favored when the cognitive trait is a crucial determinant of fitness.

Fertility control of Rattus nitidus using quinestrol: effects on reproductive organs and social behavior

Fertility control has been identified by studies in the laboratory and the field as a more appropriate and long-term control strategy for rodent pests than lethal control. In this study, we investigated the effects of quinestrol on mass of reproductive organs and on social behaviors in female and male Indochinese forest rat (Rattus andamanensis (Blyth, 1860)] using approach of morphometrics and genetics). [corrected]. A total of 16 adult females and 16 adult males were randomly assigned to 4 groups. One male and one female group were fed rice with 0.005% quinestrol by weight for 7 days, and another 2 groups were fed rice only. After 7 days, rats were assigned to 10 min dyadic encounters between groups, and investigation, aggression, defense and attack latency were quantified. All animals were killed on day 10, and reproductive organs were dissected and weighed. Dyadic encounter data showed that there were obvious changes in social behaviors of quinestrol-treated rats. Quinestrol significantly inhibited the investigative behavior of quinestrol-treated males toward control females in Rattus nitidus, but seldom affected investigation between control males and quinestrol-treated females. Aggression of control females toward quinestrol-treated males was higher than that of quinestrol-treated females, and defense of quinestrol-treated males toward control females was more remarkable than that of control males. Quinestrol remarkably decreased wet masses of epididymis and spermotophore in males and ovaries in females, but had no effect on wet masses of testes and uteri after quinestrol treatment. These results indicate that the anti-fertility effects of quinestrol on R. nitidus are attributed to not only suppressing reproductive organs but also impacting social behaviors associated with territory defense and mate choice.

Mating strategies of Pampean mouse males

Patterns of space use and sexual dimorphism are frequently used to infer mating systems. We examined body size and home range size and intra- and intersexual overlap degree in order to elucidate mating strategy of Akodon azarae males. We studied spacing patterns using 113 and 129 home ranges established by males and females, respectively, in four 0.25 ha enclosures during the breeding season. Significant differences between sexes in home range size and overlap degree were found. Male home ranges were always larger than those of females. We observed exclusive space use among males and among females. Considering only those males that shared their home ranges with females, average intersexual overlap value was about 50%. Males mainly overlap their home ranges with home ranges of two or three females. Significant differences in body size were found between males and females, with males being larger. We concluded that space use and sexual dimorphism in this species is consistent with patterns characteristic of polygynous rodents, and we propose a polygynous system in A. azarae.

Female prairie vole mate-choice is affected by the males' birth litter composition

Experimental testing and retrospective examination of breeding records were used to examine the influence of sex composition and/or size of males' birth litters on female mate-choice. Sexually naïve female prairie voles (Microtus ochrogaster) avoided males derived from all-male litters, but showed no preference for, or aversion to, males from single-male litters or from more typical mixed-sex litters. Examination of the pregnancy status of females after two weeks of pairing with a male allowed us to estimate the probabilites of a pups' intrauterine position relative to siblings for various litter sizes. The typical prairie vole pup derived from a mixed-sex litter comprised of 4.4 pups, and had a 13% chance of being isolated from siblings in utero and a 22% chance of being between siblings in utero. Pups from single-sex litters tended to be larger at weaning than did pups from mixed-sex litters; however, male size did not influence female choice behavior. These results suggest that some aspect of the perinatal experience of prairie vole pups from single sex litters can influence social interactions later in life.

Variation of telencephalon morphology of the threespine stickleback (Gasterosteus aculeatus) in relation to inferred ecology

We tested the hypothesis that increased telencephalon size has evolved in threespine stickleback fish (Gasterosteus aculeatus) from structurally complex habitats using field-caught samples from one sea-run (ancestral) and 18 ecologically diverse freshwater (descendant) populations. Freshwater habitats ranged from shallow, structurally complex lakes with benthic-foraging stickleback (benthics), to deeper, structurally simple lakes in which stickleback depend more heavily on plankton for prey (generalists). Contrary to our expectations, benthics had smaller telencephala than generalists, but the shape of the telencephalon of the sea-run and benthic populations were more convex laterally. Convex telencephalon shape may indicate enlargement of the dorsolateral region, which is homologous with the tetrapod hippocampus. Telencephalon morphology is also sexually dimorphic, with larger, less convex telencephala in males. Freshwater stickleback from structurally complex habitats have retained the ancestral telencephalon morphology, but populations that feed more in open habitats on plankton have evolved larger, laterally concave telencephala.

Male-male competition, female mate choice and their interaction: determining total sexual selection

Empirical studies of sexual selection typically focus on one of the two mechanisms of sexual selection without integrating these into a description of total sexual selection, or study total sexual selection without quantifying the contributions of all of the mechanisms of sexual selection. However, this can provide an incomplete or misleading view of how sexually selected traits evolve if the mechanisms of sexual selection are opposing or differ in form. Here, we take a two-fold approach to advocate a direction for future studies of sexual selection. We first show how a quantitative partitioning and examination of sexual selection mechanisms can inform by identifying illustrative studies that describe both male-male competition and female mate choice acting on the same trait. In our sample, the most common trait where this occurred was body size, and selection was typically linear. We found that male-male competition and female mate choice can be reinforcing or opposing, although the former is most common in the literature. The mechanisms of sexual selection can occur simultaneously or sequentially, and we found they were more likely to be opposing when the mechanisms operated sequentially. The degree and timing that these mechanisms interact have important implications for the operation of sexual selection and needs to be considered in designing studies. Our examples highlight where empirical data are needed. We especially lack standardized measures of the form and strength of selection imposed by each mechanism of sexual selection and how they combine to determine total sexual selection. Secondly, using quantitative genetic principles, we outline how the selection imposed by individual mechanisms can be measured and combined to estimate the total strength and form of sexual selection. We discuss the evolutionary consequences of combining the mechanisms of sexual selection and interpreting total sexual selection. We suggest how this approach may result in empirical progress in the field of sexual selection.

Human oestrus

For several decades, scholars of human sexuality have almost uniformly assumed that women evolutionarily lost oestrus--a phase of female sexuality occurring near ovulation and distinct from other phases of the ovarian cycle in terms of female sexual motivations and attractivity. In fact, we argue, this long-standing assumption is wrong. We review evidence that women's fertile-phase sexuality differs in a variety of ways from their sexuality during infertile phases of their cycles. In particular, when fertile in their cycles, women are particularly sexually attracted to a variety of features that likely are (or, ancestrally, were) indicators of genetic quality. As women's fertile-phase sexuality shares with other vertebrate females' fertile-phase sexuality a variety of functional and physiological features, we propose that the term oestrus appropriately applies to this phase in women. We discuss the function of women's non-fertile or extended sexuality and, based on empirical findings, suggest ways that fertile-phase sexuality in women has been shaped to partly function in the context of extra-pair mating. Men are particularly attracted to some features of fertile-phase women, but probably based on by-products of physiological changes males have been selected to detect, not because women signal their cycle-based fertility status.

The adaptive value of sociality in mammalian groups

According to behavioural ecology theory, sociality evolves when the net benefits of close association with conspecifics exceed the costs. The nature and relative magnitude of the benefits and costs of sociality are expected to vary across species and habitats. When sociality is favoured, animals may form groups that range from small pair-bonded units to huge aggregations. The size and composition of social groups have diverse effects on morphology and behaviour, ranging from the extent of sexual dimorphism to brain size, and the structure of social relationships. This general argument implies that sociality has fitness consequences for individuals. However, for most mammalian species, especially long-lived animals like primates, there are sizable gaps in the chain of evidence that links sociality and social bonds to fitness outcomes. These gaps reflect the difficulty of quantifying the cumulative effects of behavioural interactions on fitness and the lack of information about the nature of social relationships among individuals in most taxa. Here, I review what is known about the reproductive consequences of sociality for mammals.

Sex, status, and criminality: a theoretical nexus

This article offers a theoretical explanation for relationships between social status and involvement in serious and persistent criminal behavior from an evolutionary perspective. The theory's central premise is that natural selection has produced females who bias their mating choices toward males who strive for status. This bias has resulted in males devoting greater time and energy to status striving (relative to females). To account for why nearly all "victimizing" forms of criminality are more common among males than among females, the theory asserts that status striving exists along a continuum of competitive/victimizing behavior. One end of this continuum is epitomized by crude (criminal) forms of the behavior that societies generally discourage and even punish. The other end consists of sophisticated (commercial) forms that societies tolerate and even encourage. According to the theory, most males begin to exhibit non-playful forms of competitive/victimizing behavior around the onset of puberty as they start their reproductive careers. Adolescent males with the greatest abilities to learn will transition quickly from crude forms of competitive/victimizing behavior to more sophisticated forms, while males who have the greatest difficulties learning will transition more slowly. A major deduction from the theory is that genes on the Y-chromosome must be affecting the brain in ways that promote status-striving behavior. This deduction needs empirical scrutiny, although it is consistent with evidence (a) that the Y-chromosome transforms would-be ovaries into testes, the latter being specialized organs for the production of testosterone, and (b) that testosterone alters brain functioning in ways that contribute to both status striving and criminality.

Neuroecology

Neuroecology is the study of adaptive variation in cognition and the brain. The origin of neuroecology dates from the 1980s, when researchers in behavioral ecology began to apply the methods of comparative evolutionary biology to cognitive processes and the underlying neural mechanisms of cognition. The comparative approach, however, is much older. It was a mainstay of ethology, it has been part of the study of neuroanatomy since the seventeenth century, and it was used by Darwin to marshal evidence for the theory of natural selection. Neuroecology examines the relations between ecological selection pressures and species or sex differences in cognition and the brain. The goal of neuroecology is to understand how natural selection acts on cognition and its neural mechanisms. This chapter describes the general approach of neuroecology, phylogenetic comparative methods used in the field, and new findings on the cognitive mechanisms and brain structures involved in mating systems, social organization, communication, and foraging. The contribution of neuroecology to psychology and the neurosciences is the information it provides on the selective pressures that have influenced the evolution of cognition and brain structure.