Female breeding dispersal to higher quality habitats in a philopatric top predator

Philopatry and monogamy are conventionally viewed as strategies for improving fitness. Many philopatric and monogamous species have, however, been shown to perform breeding dispersal—an exchange of territory (and often also partner) between two breeding seasons. The adaptiveness of breeding dispersal remains controversial, as data remain scarce and sporadic. For the Northern Goshawk, a typically highly philopatric and monogamous forest raptor, pairs breeding in barren forest landscapes produce fewer fledglings than pairs breeding in more productive landscapes. Using data on Finnish breeding female Goshawks (Accipiter gentilis) during 1999–2016, we tested the hypotheses that: (1) breeding dispersal is more likely at barren territories, (2) dispersing females move to less barren territories, and (3) breeding dispersal improves the survival of young. About 29% of the female Goshawks in our study performed breeding dispersal, which contrasts to philopatry and suggest that site and partner fidelities show large variation within the species’ breeding range. We found no evidence that territorial landscape barrenness (proxy on habitat quality) affects the probability of breeding dispersal. However, females that dispersed upgraded to less barren territories. Nevertheless, there were no subsequent effects of breeding dispersal on reproductive performance, suggesting no obvious difference in the capability of rearing young at either site. Although dispersal events were directed to less barren habitats, we suggest that female dispersal is not driven by the pursue for more prospersous habitats, rather that those females are forced to move, for whatever reason. In addition to other observed reasons such as female–female competition for mates and loss of the original mate, intense logging of mature forests lowering local food availability and restricting nest site availability were likely a partial cause of increased breeding dispersal.

Extreme bill dimorphism leads to different but overlapping isotopic niches and similar trophic positions in sexes of the charismatic extinct huia

The New Zealand huia (Heteralocha acutirostris) had the most extreme bill sexual dimorphism among modern birds. Given the quick extinction of the species, the cause of the dimorphism could only be hypothesised to reflect different trophic niches and reduce male/female competition. We tested that hypothesis by combining museum specimens, geometric morphometrics, and isotopic analyses. We used geometric morphometrics to describe bill shape; measured bulk (δ15Nbulk) and (δ13Cbulk) values from feather as proxies of the birds’ foraging habitat and diet; and compared compound-specific stable isotopes analyses (CSIA) of nitrogen in amino acids (δ15NAA) in male–female pairs to estimate their trophic position. Sexes had significantly different, but overlapping feather δ15Nbulk and δ13Cbulk values, but δ15NAA indicated identical trophic positions and δ15Nbulk was not related to bill shape. Trophic position was less variable among females, consistent with a specialised foraging behaviour and, thus, supporting a partial male/female foraging segregation.

The Evolution of Competition

Human competition is, at least partially, responsible for some of the transcended achievements of the species (walking on the moon, the polio vaccine, etc.), but the forces unleashed by competition have also led to profound human suffering (warfare, domination of one group by another group, etc.). In this article, the authors approach competition from an evolutionary perspective, applying Darwin’s theories of natural and sexual selection to understand better the nature of human competition. From the perspective of evolutionary psychology, humans engage in competition to gain resources, including status, food, and mating opportunities. Males tend to engage in more overt and aggressive forms of competition than females, but both sexes desire access to material and cultural goods associated with reproductive fitness. In the last roughly seventy years, the nature of men’s competition has transformed dramatically leading to declines in both within and between-group violence. As developed societies have succeeded in suppressing more overt and destructive forms of male–male competition, men attempt to gain status through occupational success, cognitive sophistication, moral signaling, and other relatively nonviolent behaviors. In this sense, men’s and women’s competition is more similar than it was a century ago. However, women’s competition is still less visible and relies on more indirect mechanisms (e.g., spreading gossip, subtle use of body language). For this reason, female–female competition has attracted less study than male–male competition. Fortunately, in the last decade, psychologists have partially redressed this imbalance.

The effect of dominance rank on female reproductive success in social mammals

Life in social groups, while potentially providing social benefits, inevitably leads to conflict among group members. In many social mammals, such conflicts lead to the formation of dominance hierarchies, where high-ranking individuals consistently outcompete other group members. Given that competition is a fundamental tenet of the theory of natural selection, it is generally assumed that high-ranking individuals have higher reproductive success than lower-ranking individuals. Previous reviews have indicated large variation across populations on the potential effect of dominance rank on reproductive success in female mammals. Here, we perform a meta-analysis based on 444 effect sizes from 187 studies on 86 mammal species to investigate how life-history, ecology and sociality modulate the relationship between female dominance rank and fitness. We show that (1) dominance rank is generally positively associated with reproductive success, independent of the approach different studies have taken to answer this question; (2) life-history mechanisms mediate the relationship between rank and reproductive success, with higher effects of dominance rank on reproductive output than on survival, particularly in species with high reproductive investment; (3) the fitness benefits to high-ranking females appear consistent across ecological conditions, and (4) instead the social environment consistently mitigates rank differences on reproductive success by modulating female competition.

Evolution of nuptial gifts and its coevolutionary dynamics with male-like persistence traits of females for multiple mating

Background Many male animals donate nutritive materials during courtship or mating to their female mates. Donation of large-sized gifts, though costly to prepare, can result in increased sperm transfer during mating and delayed remating of the females, resulting in higher paternity. Nuptial gifting sometimes causes severe female-female competition for obtaining gifts (i.e., sex-role reversal in mate competition) and selection on females to increase their mating rate, changing the intensity of sperm competition and the resultant paternity gains. We built a theoretical model to simulate such coevolutionary feedbacks between nuptial gift size (male trait) and propensity for multiple mating (female trait). Donation of nuptial gifts sometimes causes development of female persistence trait for gift acquisition. We also analyzed the causes and consequences of this type of traits, taking double receptacles for nutritious seminal gifts, which are known to occur in an insect group with a “female penis” (Neotrogla spp.), as an illustrative example. Results Our individual-based simulations demonstrated that female-female competition for male-derived nutrients always occur when the environment is oligotrophic and mating costs are low for females. However, a positive correlation between donated gift size and the resultant paternity gain was a requisite for the co-occurrence of large gifts and females’ competitive multiple mating for the gifts. When gift donation satisfied female demands and thus resulted in monandry, exaggeration of nuptial gift size also occurred under the assumption that the last male monopolizes paternity. The evolution of double slots for gift acquisition and digestion (female persistence trait) always occurred when males could not satisfy the demands of females for gifts. However, through coevolutionary reduction in male gift size, fixation of this trait in a population drastically reduced the average female fitness. Conclusion Sperm usage patterns, which have rarely been examined for animals with nuptial gifts, can be a critical factor for determining the extent of exaggeration in nuptial gifting. Sex-role reversals in mate competition, as a result of donation of nuptial gifts from males to females, can involve the evolution of male-like, persistent traits in females that reduce population productivity, as is the case with persistence traits in males.

Egg size variation in a long-lived polyandrous shorebird in the context of senescence and breeding phenology

Anisogamy is a central component of sex role evolution, however, the effect of female-female mating competition on egg size variation in polyandrous species is unclear. Moreover, egg size may also be shaped by age-dependent trade-offs between reproductive investments and somatic maintenance that are responsible for senescence. Here we investigate how mating behaviour and senescence are associated with egg size variation in female snowy plovers (Charadrius nivosus). Snowy plovers are long-lived shorebirds (longevity record: 20 years) that often produce several nests each year, with females either sequentially changing partners between breeding attempts or remaining monogamous between attempts. We examined how age, seasonality, body size, and mating behaviour relate to within- and between-female variation in egg volume using repeated measures collected over a 15-year period. We found no evidence of reproductive senescence in egg volume in snowy plover females. Rather, egg volume, polyandry, and re-nesting were strongly linked to breeding phenology: early breeding females had a higher likelihood of being polyandrous or replacing failed clutches, yet these individuals laid smaller eggs likely due to physiological limitations associated with the early season. Older individuals and local recruits secured the earliest breeding opportunities in the season suggesting that prior experience could give an edge in the female-female competition for mates. Larger females laid the largest eggs, as expected, but there was no relationship between body size and lay date - implying that size may not provide an advantage in female-female competition. Our findings highlight the existence of several direct and indirect constraints on female reproductive investment that likely shape individual variation in lifetime reproductive success. Future research investigating reproductive senescence of wild populations should consider mating system dynamics when examining variation in reproductive investment.

SPAWNING OF BLACK GHOST KNIFEFISH, Apteronotus albifrons WITH DIFFERENT SEX RATIOS

Black ghost knifefish, Apteronotus albifrons, is a South America-introduced ornamental fish species that has been widely cultivated in Indonesia. Some farmers breed this fish with different sex ratios, but the optimum sex ratio remains unclear. This study aimed to evaluate the spawning behavior and reproductive performance of black ghost knifefish with different sex ratios. The treatments in this study were arranged in a completely randomized design consisting of different sex ratios between males and females, namely: A (one male : three females), B (two males : three females), and C (three males : three females). Each treatment was done in triplicate. The broodstock were maintained in an aquarium (80 cm x 40 cm x 40 cm) and fed with bloodworm twice a day. The water was changed every day as much as 60% of the total volume. During the experiment, the parameters of spawning behavior, number of fish spawning, number of eggs, fertilization rate, hatching rate, and daily spawning frequencies were observed. The observation was done for seven days. The study results showed that black ghost knifefish spawned at night (11 pm - 2 am). The mating and spawning occurred between one male and one female. Competition between males was observed in the treatments indicated by aggressive movements of a male toward the others, such as sudden approaching, chasing, and driving away the others. Fish in treatment-B spawned consistently from day-1 to day-5. Fish in treatment-A spawned from day-2 to day-4, while fish in treatment-C spawned only on day-7. The reproductive performance parameters showed no significant difference in all treatments except the hatching rate parameter of treatment-B. The study concludes that better reproductive performance of black ghost knifefish, A. albifrons can be achieved with a spawning ratio of two males and three females. Further research on individual and mass spawning methods with the best spawning ratio of the fish is required.

Male Choice, Female Competition, and Female Ornaments in Sexual Selection

When Darwin first proposed sexual selection theory he suggested two mechanisms: competition among males and choice by females. There is no doubt that these mechanisms are immensely important, but their mirror images have been largely underappreciated so far. In fact, males choose as well and females compete. Males choose based on female quality, often selecting mating partners that are more fecund. But male choice is also associated with changes in the sex ratio of a population and males can be choosy when they are rare. Furthermore, males sometimes invest heavily into reproduction and that too can be associated with male choice. That females compete with another, although less often with open aggression, is another understudied phenomenon. Finally, we now know that females are often ornamented, but are these ornaments under sexual selection by males? This book tries to review what we know and point to what we don’t know while pointing out the connections between male mate choice and female competition for a more complete view of sexual selection.

Female–Female Competition

There is no disagreement that males compete over access to reproductive opportunities. This competition can be covert or take the form of physical fights, which are easily observed in many species. Males take considerable risks when they fight, presumably because the price—access to reproduction—is so high. But what about females? They also often compete for males, but in less risky ways. They also seem to compete less directly for individual males, but more indirectly for resources that males can provide. Nonetheless, female competition is more important in shaping sexual selection than previously thought.