Adult sex ratio variation: implications for breeding system evolution

Adult sex ratio (ASR) exhibits immense variation in nature, although neither the causes nor the implications of this variation are fully understood. According to theory, the ASR is expected to influence sex roles and breeding systems, as the rarer sex in the population has more potential partners to mate with than the more common sex. Changes in mate choice, mating systems and parental care suggest that the ASR does influence breeding behaviour, although there is a need for more tests, especially experimental ones. In the context of breeding system evolution, the focus is currently on operational sex ratios (OSRs). We argue that the ASR plays a role of similar importance and urge researchers to study the ASR and the OSR side by side. Finally, we plead for a dynamic view of breeding system evolution with feedbacks between mating, parenting, OSR and ASR on both ecological and evolutionary time scales.     

Three-dimensional geometric morphometric analysis of the skull of Protoceratops andrewsi supports a socio-sexual signalling role for the ceratopsian frill

Socio-sexual selection is predicted to be an important driver of evolution, influencing speciation, extinction and adaptation. The fossil record provides a means of testing these predictions, but detecting its signature from morphological data alone is difficult. There are, nonetheless, some specific patterns of growth and variation which are expected of traits under socio-sexual selection. The distinctive parietal-squamosal frill of ceratopsian dinosaurs has previously been suggested as a socio-sexual display trait, but evidence for this has been limited. Here, we perform a whole-skull shape analysis of an unprecedentedly large sample of specimens of Protoceratops andrewsi using a high-density landmark-based geometric morphometric approach to test four predictions regarding a potential socio-sexual signalling role for the frill. Three predictions—low integration with the rest of the skull, significantly higher rate of change in size and shape during ontogeny, and higher morphological variance than other skull regions—are supported. One prediction, sexual dimorphism in shape, is not supported, suggesting that sexual differences in P. andrewsi are likely to be small. Together, these findings are consistent with mutual mate choice or selection for signalling quality in more general social interactions, and support the hypothesis that the frill functioned as a socio-sexual signal in ceratopsian dinosaurs.     

The causes and implications of sex role diversity in shorebird breeding systems

Males and females often exhibit different behaviours during mate acquisition, pair-bonding and parenting, and a convenient label to characterize these behaviours is sex role. The diverse roles that male and female shorebirds (plovers, sandpipers and allies) exhibit in mating and parenting have played a key role in advancing mainstream theories in avian ecology and behavioural biology including sexual selection, sexual conflict and parental cooperation. Recent advances in shorebird research have also highlighted the significance of the social environment in driving sex role behaviours by linking the adult sex ratio with breeding behaviour and population demography. Here we review the key advances in sex role research using shorebirds as an ecological model system. We identify knowledge gaps and argue that shorebirds have untapped potential to accelerate diverse research fields including evolutionary genomics, movement ecology, social networks and environmental changes. Future studies of sex roles will benefit from individual-based monitoring using advanced tracking technologies, and from multi-team collaborations that are facilitated by standardized data collection methodologies across different species in the field. These advances will not only contribute to our understanding of reproductive strategies, but they will also have knock-on effects on predicting population resilience to environmental changes and on prioritizing species for conservation.     

Acoustic communication in crocodilians: from behaviour to brain

Crocodilians and birds are the modern representatives of Phylum Archosauria. Although there have been recent advances in our understanding of the phylogeny and ecology of ancient archosaurs like dinosaurs, it still remains a challenge to obtain reliable information about their behaviour. The comparative study of birds and crocodiles represents one approach to this interesting problem. One of their shared behavioural features is the use of acoustic communication, especially in the context of parental care. Although considerable data are available for birds, information concerning crocodilians is limited. The aim of this review is to summarize current knowledge about acoustic communication in crocodilians, from sound production to hearing processes, and to stimulate research in this field. Juvenile crocodilians utter a variety of communication sounds that can be classified into various functional categories: (1) “hatching calls”, solicit the parents at hatching and fine‐tune hatching synchrony among siblings; (2) “contact calls”, thought to maintain cohesion among juveniles; (3) “distress calls”, induce parental protection; and (4) “threat and disturbance calls”, which perhaps function in defence. Adult calls can likewise be classified as follows: (1) “bellows”, emitted by both sexes and believed to function during courtship and territorial defence; (2) “maternal growls”, might maintain cohesion among offspring; and (3) “hisses”, may function in defence. However, further experiments are needed to identify the role of each call more accurately as well as systematic studies concerning the acoustic structure of vocalizations. The mechanism of sound production and its control are also poorly understood. No specialized vocal apparatus has been described in detail and the motor neural circuitry remains to be elucidated. The hearing capabilities of crocodilians appear to be adapted to sound detection in both air and water. The ear functional anatomy and the auditory sensitivity of these reptiles are similar in many respects to those of birds. The crocodilian nervous system likewise shares many features with that of birds, especially regarding the neuroanatomy of the auditory pathways. However, the functional anatomy of the telencephalic auditory areas is less well understood in crocodilians compared to birds.     

The goals of direct paternal care among a South Amerindian population

Human males are remarkable among mammals in the level of investment they provide to their wives and children. However, there has been debate as to the degree to which men actually invest and through which fitness pathways the benefits of familial investment are realized. Much of the previous research exploring these issues has focused on men's roles as providers, but few have explored correlates of men's direct parental care. Although this is reasonable given men's parental emphasis on provisioning, the providing of direct care is more straightforward with a clear provider and recipient and little ambiguity as to the care‐giver's intent. Here, we explore contextual correlates of men's direct care among the Tsimane of Bolivia to determine the extent to which such care is patterned to enhance its effectiveness in increasing child wellbeing and the efficient functioning of the family. We also explore whether Tsimane fathers provide care in ways that enhance the positive effect it has on the wife's perception of the care provider. Overall, we find that Tsimane men appear responsive to the needs of children and the family, but show that there is little evidence that men respond to factors expected to increase the impact that men's care has on their reputations with their wives. Am J Phys Anthropol 2009. © 2009 Wiley‐Liss, Inc.     

The evolution of human biosocial behaviour

The analysis of human behaviour can be approached from three different but complementary perspectives: the first includes the eternal debate about the degree of environmental or genetic determinism of social behaviour; the second, in the context of evolutionary ecology, concerns the evaluation of behavioural responses to morphological and/or environmental changes that have been the key to success in our species; the third, in the context of the analysis of the biology of the health of modern day populations, deals with the biological consequences of social behavioural changes. The secret of the success of a species resides in its capacity to respond behaviourally to the morphological and environmental changes produced during its biological history. What is unique about humans concerns our brains and their derived function: flexible behaviour. The morphological, physiological and behavioural changes that allow thecreation and maintenance of such a large brain are intimately connected to reproduction and therefore to the biosociology of women, the members of the speciesHomo sapiens in whom are combined, with notable success, a prolonged life-cycle, some anatomical and physiological traits and flexible reproductive behaviour, which together confer a decisive demographic advantage on them over other hominids. In summary, as well as contributing to the spread of this information by which women can make informed decisions based on a knowledge of causes, with the aim of optimizing our health it is necessary to consider the possibility of approaching some aspects of our biology and behaviour as patterns fixed by evolution. Three factors would be the most easily adjustable for this purpose: a) to delay the age of sexual maturation, b) to bring forward the age of first maternity, and c) to encourage breastfeeding on demand without substitutes and for a 3–5 month period.     

The tarsus of erythrosuchid archosaurs, and implications for early diapsid phylogeny

The morphology of the erythrosuchid ankle joint is reassessed. Two specimens, recently thought to have been incorrectly referred to Erythrosuchus africanus , are shown without doubt to belong to this taxon. Furthermore, the morphology is essentially similar to that of other early archosaurs. The tarsus of Erythrosuchus is poorly ossified and consists of a calcaneum, astragalus, and two distal tarsals. The calcanea of Erythrosuchus, Vjushkovia triplicostata , and Shansisuchus shansisuchus are all similar in being dorsoventrally compressed, possessing a lateral tuber, and lacking a perforating foramen. The astragalus of V. triplicostata is currently unknown. The astragalus of Shansisuchus is apparently unique in form. The erythrosuchid pes is therefore more derived than has been recently proposed. The tarsal morphology of several other archosauromorph taxa is reviewed and many details are found to be at variance with the literature. The plesiomorphic condition for the Archosauromorpha consists of four distal tarsals and a proximal row of three elements; two of which articulate with the tibia. These proximal elements are interpreted as the astragalus, calcaneum, and a centrale, and the same pattern is retained in the earliest archosaurs. This reassessed tarsal morphology has implications for the homology of the centrale and reconstruction of early diapsid phylogeny.     

Sex differences in provisioning rules: responses of Manx shearwaters to supplementary chick feeding

Sex differences in food provisioning have been found in a numberof socially monogamous birds with biparental care, but the reasonsremain unclear. In Manx shearwaters, males provide 40–50%more food for chicks than do females, and previous empiricaldata have suggested that this difference could arise becausefemales are able to regulate food delivery by reducing the provisioningof well-nourished chicks, whereas males are not (hypothesis1). Alternatively, however, males may be as capable as femalesof assessing and responding to the variation in the nutritionalrequirements of their chick but have a higher threshold forreducing food delivery to well-nourished chicks (hypothesis2). To test these two hypotheses, we used supplementary feedingto manipulate the nutritional status of chicks and then examinedthe responses of male and female parents and their offspring.Supplementary feeding significantly reduced both the beggingbehavior of chicks and the frequency and sizes of meals deliveredby parents. Males and females reduced their overall provisioningrates to a similar extent (males by 38%, females by 42%), somaintaining the same difference in contributions to provisioningin the control group (males 58%, females 42%) and the experimentaltreatment (males 59%, females 41%). These data strongly supporthypothesis 2. Supplementary feeding of chicks resulted in fewervisits by parents and a higher proportion of long trips in bothsexes (4 days for males, 5–7 days for females). However,maximum trip durations were unchanged, suggesting that supplementaryfeeding of chicks had no effect on the foraging ranges or overallfood-provisioning strategies of parents.     

First trace and body fossil evidence of a burrowing, denning dinosaur

A fossil discovery in the mid-Cretaceous Blackleaf Formation of southwest Montana, USA, has yielded the first trace and body fossil evidence of burrowing behaviour in a dinosaur. Skeletal remains of an adult and two juveniles of Oryctodromeus cubicularis gen. et sp. nov. a new species of hypsilophodont-grade dinosaur, were found in the expanded distal chamber of a sediment-filled burrow. Correspondence between burrow and adult dimensions supports Oryctodromeus as the burrow maker. Additionally, Oryctodromeus exhibits features of the snout, shoulder girdle and pelvis consistent with digging habits while retaining cursorial hindlimb proportions. Association of adult and young within a terminal chamber provides definitive evidence of extensive parental care in the Dinosauria. As with modern vertebrate cursors that dig, burrowing in Oryctodromeus may have been an important adaptation for the rearing of young. Burrowing also represents a mechanism by which small dinosaurs may have exploited the extreme environments of polar latitudes, deserts and high mountain areas. The ability among dinosaurs to find or make shelter may contradict some scenarios of the Cretaceous-Paleogene impact event. Burrowing habits expand the known range of nonavian dinosaur behaviours and suggest that the cursorial ancestry of dinosaurs did not fully preclude the evolution of different functional regimes, such as fossoriality.     

Ecology of giant water bugs (Hemiptera: Heteroptera: Belostomatidae)

Giant water bugs (Heteroptera: Belostomatidae) are aquatic predators of freshwater habitats, and include ca. 150 species distributed throughout the world's subtropical and tropical areas. They have unique mating systems, which involve female competition, and exhibit paternal care, wherein males attend eggs laid by the females on emergent plants (Lethocerinae) or on their backs (Belostomatinae). I review here the studies on the predator–prey relationships, morphology, migration, mating behavior and conservation of this family of insects.     

The Relationship of Spawning Mode to Conservation of North American Minnows (Cyprinidae)

Approximately 20% of North American minnows are considered imperiled. The factors responsible for imperilment in this group are complex, but the relationship of spawning mode to conservation of North American minnows has not been explored. I provide a summary of the spawning modes of imperiled North American minnows, discuss patterns between these modes and conservation status, and predict the spawning modes for several poorly-known imperiled species. Of the 46 species of North American minnows that are imperiled, spawning modes are known for only 13 species. All spawning modes are represented in the imperiled group of minnows except mound-building and egg-clustering, and with the exception of crevice-spawners and pit-ridge-builders, the percentage of imperiled minnows in each category of spawning mode is roughly proportional to the percentage of minnows in that category overall. Species with complex spawning modes, such as mound-building, pit-building and egg-clustering, are among the most common fishes in North American streams. This pattern suggests that there is a relationship between parental care and success (lack of imperilment) in minnows. Spawning mode is an important consideration in the formulation of recovery plans and proactive conservation efforts.     

The evolution of crocodilian nesting ecology and behavior

Crocodilians comprise an ancient and successful lineage of archosaurs that repeatedly raises questions on how they survived a mass extinction and remained relatively unchanged for ~100 million years. Was their success due to the change‐resistant retention of a specific set of traits over time (phylogenetic conservatism) or due to flexible, generalist capabilities (e.g., catholic diets, phenotypic plasticity in behavior), or some combination of these? We examined the evolution of reproductive ecology and behavior of crocodilians within a phylogenetic perspective, using 14 traits for all 24 species to determine whether these traits were phylogenetically constrained versus (ecologically) convergent. Our analysis revealed that the ancestral crocodilian was a mound nester that exhibited both nest attendance and defense. Nesting mode exhibited 4–5 transformations from mound to hole nesting, a convergence of which habitat may have been a driving factor. Hole nesters were more likely to nest communally, but this association may be biased by scale. Although there were exceptions, mound nesters typically nested during the wet season and hole nesters during the dry season; this trait was relatively conserved, however. About two‐thirds of species timed their nesting with the wet season, while the other third timed their hatching with the onset of the wet season. Nest attendance and defense were nearly ubiquitous and thus exhibited phylogenetic conservatism, but attendance lodging was diverse among species, showing multiple reversals between water and burrows. Collectively, our analysis reveals that reproductive trait evolution in crocodilians reflects phylogenetic constraint (nest attendance, nest defense), ecological convergence (seasonal timing of nesting, nest attendance lodging), or both (mode of nesting). Some traits (e.g., communal nesting and mode of nesting) were autocorrelated. Our analysis provides a framework for addressing hypotheses raised for why there has been trait convergence in reproductive ecology and behavior in crocodilians and why some traits remained phylogenetically conserved.     

Anisogamy selects for male-biased care in self-consistent games with synchronous matings

We reexamine the influential parental investment hypothesis proposed by Trivers for the causal relationship between anisogamy and widespread female-biased parental care. We build self-consistent versions of Maynard Smith's simple evolutionary game between males and females over parental care, and incorporate consequences of anisogamy for gamete production and its trade-off with parental care, and for patterns of mate limitation. As male mating opportunities are limited by females, frequency-dependent selection acts on male strategies. Assuming synchrony of matings in the population, our analytical models find either symmetric sex roles or male-biased care as an evolutionarily stable strategy (ESS), in contrast to Trivers' hypothesis. We simulate evolution in asynchronously mating populations and find that diverse parental roles, including female care, can be ESS depending on the parameters. When caring males can also remate, or when females can increase the clutch size by deserting, there is stronger selection for male-biased care. Hence, we argue that the mating-caring trade-off for males is neither a necessary consequence of anisogamy nor sufficient to select for female-biased care. Instead, the factors excluded from our models—costly competitive traits, sexual selection, and partial parentage—may be necessary for the parental investment hypothesis to work.     

Sexual reproduction in Daphnia pulex (Crustacea: Cladocera): observations on male mating behaviour and avoidance of inbreeding

1.  Mating behaviour in Daphnia appears to rely on random contact between males and sexual females rather than diffusible pheromones. Males may be able to discriminate sexually receptive females from females in other developmental stages and increase their mating efficiency. Males may also use chemical signals to avoid mating with females from the same clone and avoid the severe inbreeding depression that has been documented for intraclonal mating. The present study used experiments to test for the avoidance of intraclonal mating and assess male mating efficiency in D. pulex .
2.  Three clones were examined for the avoidance of intraclonal mating by providing males with an opportunity to mate with females of the same or two different clones. The proportion of intraclonal matings did not differ from the proportion of interclonal matings, suggesting that D. pulex males do not use kin discrimination to avoid mating with females from the same clone.
3.  The proportion of mated females decreased with increasing numbers and density of sexual females when exposed to a single male. This observation suggests that a male spends more time pursuing and copulating with sexually receptive females than non-receptive females and there is insufficient time to mate with all sexual females. The decrease in proportion of females mated could also be the result of sperm depletion in the male. Sperm depletion is unlikely to occur in nature because sexually receptive females are much rarer than in the experimental conditions.     

Factors affecting the duration of nest defense and reproductive lifespan of female sockeye salmon, Oncorhynchus nerka

Reproductive success of female animals is often affected by a combination of fecundity and parental care. In female salmonid fishes, acquisition of nest (redd) sites and prevention of their use by other females are critical to reproductive success. These factors are particularly important for stocks that spawn at high densities. Body size is positively correlated with fecundity and egg size, and has been hypothesized to control the outcome of intrasexual competition and longevity. We tested this hypothesis by evaluating the influences of body size, intrasexual aggression and arrival date on duration and success of redd guarding by female sockeye salmon, Oncorhynchus nerka, in a small Alaskan creek. Contrary to the hypothesis, larger females guarded their redds no longer than smaller females, and did not live as long in the stream. Aggression was not related to body size or overall longevity but was positively correlated with residence period on the redd. Females that entered the creek earlier lived longer, spent longer on their redds, and spent more time guarding their redds after spawning than females that entered the creek later. However, despite their longevity, early-arriving fish were more likely to have their redds reused by another female because they died before all the females had selected redd sites. The small average body size in this stock is consistent with weak selection for large size, and with our evidence that size provided little if any advantage in nest guarding.     

Predatory risk increased due to egg‐brooding in Armadillidium vulgare (Isopoda: Oniscidea)

Cost of reproduction is associated with a reduction in subsequent survival or future breeding success. A decrease in survival rate of parents during or after reproduction reduces the probability of their future reproduction. However, few studies have demonstrated such survival costs to parents. Females of Armadillidium vulgare hold their eggs in a marsupium and brood these until the young hatch. Caring for eggs in a marsupium seems to place a large burden on brooding females, and it restricts their predator avoidance behaviour. As such, costs of care may increase the mortality rates of brooding females. To reveal the costs of parental care, we examined the effects of egg brooding on behaviour and predation risk. Egg‐brooding females decreased speed of locomotion and rolling duration, and were killed by predators at a higher rate. Our results indicate that egg brooding in A. vulgare has costs in the form of predation risk.