In many species, intense male-male competition for the opportunity to sire offspring has led to the evolution of selfish reproductive traits that are harmful to the females they mate with. In the ...fruit fly, Drosophila melanogaster, males modulate their reproductive behavior based on the perceived intensity of competition in their premating environment. Specifically, males housed with other males subsequently transfer a larger ejaculate during a longer mating compared to males housed alone. Although the potential fitness benefits to males from such plasticity are clear, its effects on females are mostly unknown. Hence, we tested the long-term consequences to females from mating with males with distinct social experiences. First, we verified that competitive experience influences male mating behavior and found that males housed with rivals subsequently have shorter mating latencies and longer mating durations. Then, we exposed females every other day for 20 days to males that were either housed alone or with rivals, and subsequently measured their fitness. We found that females mated to males housed with rivals produce more offspring early in life but fewer offspring later in life and have shorter lifespans but similar intrinsic population growth rates. These results indicate that plasticity in male mating behavior can influence female life histories by altering females’relative allocation to early versus late investment in reproduction and survival.
The presence of social cues of reproductive competition can favour plasticity in reproductive traits and strategies. However, whether these types of social cues may also lead to transgenerational ...plasticity via maternal effects has scarcely been investigated. To test this hypothesis, I exposed adult female crickets, Gryllus bimaculatus, to either a low or a high density of intermale competition cues during the period of egg formation by altering the density of males in the surrounding environment. Then, I assessed how the experimental manipulation affected the reproductive strategies of male offspring by quantifying their relative investment in sexual signalling, courtship behaviours and sperm production. The results revealed that males whose mothers were exposed to a high density of males invested less in calling for potential mates in adulthood but interestingly when they had access to a mate, they courted her more intensively than males of mothers exposed to a low density of males. Yet, offspring sperm production was unaffected by the experimental treatment, suggesting that the maternal influence on offspring traits under postcopulatory sexual selection may be weaker. Overall, my findings highlight the role of socially mediated maternal effects in promoting transgenerational plasticity in different offspring reproductive traits and the possibility that offspring reproductive strategies may be under, at least partially, maternal influence.
•Males of mothers exposed to a high density of males invested less in calling.•When males had access to a female, they courted her more intensively.•Male sperm production was unaffected by the maternal sociosexual environment.•Socially mediated maternal effects can influence offspring reproductive strategies.
The inverse relationship between body size and vocalization pitch has been described in a number of species. Nevertheless, the existence of size–pitch allometry within any songbird species is ...surprising due to the small size variation between males, the determinate growth and exceptional vocal prowess of the taxon. The phenomenon has been documented in only a few songbird species so far and the consequences of allometry remain unclear in this taxonomic group. In this study, we provide evidence that song spectral features are related to one of the body size components (tarsus length) even in a very small songbird species: the willow warbler, Phylloscopus trochilus. Moreover, the response of territorial males was affected by the pitch asymmetry between the subject and the playback stimulus: the lower-pitched the subject's song in respect to the stimulus the bolder was its response. Our results suggest that willow warbler males may use song pitch to assess the body size of their rivals (i.e. their fighting ability) in male–male competition for resources.
•Size-pitch allometry is little studied in songbirds.•We revealed size-pitch allometry in songs of a small songbird: the willow warbler.•Bigger males (tarsus as proxy for body size) had lower songs.•Males' responses covaried with pitch asymmetry between subject and stimulus.•Males kept further from and were more active with stimuli representing bigger threat.
Sexual size dimorphism (SSD) is a common morphological trait in ungulates, with polygyny considered the leading driver of larger male body mass and weapon size. However, not all polygynous species ...exhibit SSD, while molecular evidence has revealed a more complex relationship between paternity and mating system than originally predicted. SSD is, therefore, likely to be shaped by a range of social, ecological and physiological factors. We present the first definitive analysis of SSD in the common hippopotamus (
) using a unique morphological dataset collected from 2994 aged individuals. The results confirm that hippos exhibit SSD, but the mean body mass differed by only 5% between the sexes, which is rather limited compared with many other polygynous ungulates. However, jaw and canine mass are significantly greater in males than females (44% and 81% heavier, respectively), highlighting the considerable selection pressure for acquiring larger weapons. A predominantly aquatic lifestyle coupled with the physiological limitations of their foregut fermenting morphology likely restricts body size differences between the sexes. Indeed, hippos appear to be a rare example among ungulates whereby sexual selection favours increased weapon size over body mass, underlining the important role that species-specific ecology and physiology have in shaping SSD.
Intrasexually selected weapons Rico‐Guevara, Alejandro; Hurme, Kristiina J.
Biological reviews of the Cambridge Philosophical Society,
February 2019, Letnik:
94, Številka:
1
Journal Article
Recenzirano
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ABSTRACT
We propose a practical concept that distinguishes the particular kind of weaponry that has evolved to be used in combat between individuals of the same species and sex, which we term ...intrasexually selected weapons (ISWs). We present a treatise of ISWs in nature, aiming to understand their distinction and evolution from other secondary sex traits, including from ‘sexually selected weapons’, and from sexually dimorphic and monomorphic weaponry. We focus on the subset of secondary sex traits that are the result of same‐sex combat, defined here as ISWs, provide not previously reported evolutionary patterns, and offer hypotheses to answer questions such as: why have only some species evolved weapons to fight for the opposite sex or breeding resources? We examined traits that seem to have evolved as ISWs in the entire animal phylogeny, restricting the classification of ISW to traits that are only present or enlarged in adults of one of the sexes, and are used as weapons during intrasexual fights. Because of the absence of behavioural data and, in many cases, lack of sexually discriminated series from juveniles to adults, we exclude the fossil record from this review. We merge morphological, ontogenetic, and behavioural information, and for the first time thoroughly review the tree of life to identify separate evolution of ISWs. We found that ISWs are only found in bilateral animals, appearing independently in nematodes, various groups of arthropods, and vertebrates. Our review sets a reference point to explore other taxa that we identify with potential ISWs for which behavioural or morphological studies are warranted. We establish that most ISWs come in pairs, are located in or near the head, are endo‐ or exoskeletal modifications, are overdeveloped structures compared with those found in females, are modified feeding structures and/or locomotor appendages, are most common in terrestrial taxa, are frequently used to guard females, territories, or both, and are also used in signalling displays to deter rivals and/or attract females. We also found that most taxa lack ISWs, that females of only a few species possess better‐developed weapons than males, that the cases of independent evolution of ISWs are not evenly distributed across the phylogeny, and that animals possessing the most developed ISWs have non‐hunting habits (e.g. herbivores) or are faunivores that prey on very small prey relative to their body size (e.g. insectivores). Bringing together perspectives from studies on a variety of taxa, we conceptualize that there are five ways in which a sexually dimorphic trait, apart from the primary sex traits, can be fixed: sexual selection, fecundity selection, parental role division, differential niche occupation between the sexes, and interference competition. We discuss these trends and the factors involved in the evolution of intrasexually selected weaponry in nature.
Summary
Divergence in sexually selected traits in allopatry should affect the degree and direction of hybridization. However, few studies have established the causes and targets of sexual selection ...during secondary contact.
Common wall lizards (Podarcis muralis) from north‐central Italy have highly exaggerated male sexual traits compared to populations in Western Europe. Using experimental populations, we show that this creates asymmetries in male dominance, spatial habitat use and reproductive success upon secondary contact. Hybridization occurred almost exclusively between males of the Italian lineage and females of the Western European lineage.
We provide evidence to suggest stronger ongoing selection on male sexual traits within the dominant Italian lineage. However, these same characters did not predict hybridization, and hybrid matings contributed little to variance in male reproductive success. Instead, most hybrid offspring were sired by Italian males displaying phenotypes associated with lower within‐lineage reproductive success.
Thus, highly directional hybridization arises because some Italian males are out‐competed within their own lineage but remain competitive relative to males of the other lineage.
This pattern of hybridization is consistent with the direction of introgression in natural contact zones, but our data suggest that sexual selection acting through hybridization may be weak at the leading edge of natural hybrid zones.
A lay summary is available for this article.
Lay Summary
Many species often show male–male combat for mating opportunities and resources within the species. Sexual selection through this radical combat leads to the evolution of males with exaggerated ...traits used as weapons, such as horns or mandibles, that often result in victory during combat. However, heterospecific interaction due to errors in species identification has often been observed, which results in decreased mating opportunities within the same species and fewer fertilized eggs. Males with exaggerated weapons may show dominance in resource acquisition over males without weapons and may decrease the reproductive success of the latter due to competition between the two. However, few studies have examined heterospecific interaction focusing on males with or without weapons. In this study, we investigated the effects of the male weapon on reproductive traits in heterospecific interaction in two species: the broad‐horned flour beetle (Gnatocerus cornutus), in which males have exaggerated weapon traits; and the red flour beetle (Tribolium castaneum), in which males have no weapon traits. Both species are closely related and use the same food resources. G. cornutus males interfered with the resource acquisition and reproductive opportunities of T. castaneum by attacking T. castaneum. The reproductive success of T. castaneum decreased when they cohabited with G. cornutus males. These findings show that male weapon traits, which are important for sexual selection within the same species, can also greatly influence reproduction in other species.
Weapon traits possessed by males of many species play an important role in male–male combat for reproduction, but it was unclear whether they affect reproduction in other species. We compared the reproductive success of each other using Gnatocerus cornutus, whose males have the weapon, and its close relative, Tribolium castaneum, whose males do not have weapon. We found that the presence of G. cornutus males reduced the reproductive success of T. castaneum, but not vice versa.
Protective buttressing of the hominin face Carrier, David R.; Morgan, Michael H.
Biological reviews of the Cambridge Philosophical Society,
February 2015, Letnik:
90, Številka:
1
Journal Article
Recenzirano
ABSTRACT
When humans fight hand‐to‐hand the face is usually the primary target and the bones that suffer the highest rates of fracture are the parts of the skull that exhibit the greatest increase in ...robusticity during the evolution of basal hominins. These bones are also the most sexually dimorphic parts of the skull in both australopiths and humans. In this review, we suggest that many of the facial features that characterize early hominins evolved to protect the face from injury during fighting with fists. Specifically, the trend towards a more orthognathic face; the bunodont form and expansion of the postcanine teeth; the increased robusticity of the orbit; the increased robusticity of the masticatory system, including the mandibular corpus and condyle, zygoma, and anterior pillars of the maxilla; and the enlarged jaw adductor musculature are traits that may represent protective buttressing of the face. If the protective buttressing hypothesis is correct, the primary differences in the face of robust versus gracile australopiths may be more a function of differences in mating system than differences in diet as is generally assumed. In this scenario, the evolution of reduced facial robusticity in Homo is associated with the evolution of reduced strength of the upper body and, therefore, with reduced striking power. The protective buttressing hypothesis provides a functional explanation for the puzzling observation that although humans do not fight by biting our species exhibits pronounced sexual dimorphism in the strength and power of the jaw and neck musculature. The protective buttressing hypothesis is also consistent with observations that modern humans can accurately assess a male's strength and fighting ability from facial shape and voice quality.
Sexual coercion is widespread in the animal kingdom. Its direct forms, including harassment and forced copulation, have largely been investigated as an expression of (alternative) male reproductive ...strategies, rather than the result of a sexual conflict between the sexes. Likewise, the frequent occurrence of forced copulations in orang-utans (Pongo spp.) has been attributed to male strategies and more recently also to concealed female fecundity. So far, however, the immediate contextual variables leading to forced copulations have rarely been examined. We compared two orang-utan populations, Suaq (Pongo abelii, Sumatra) and Tuanan (Pongo pygmaeus, Borneo), both characterized by an individual-based fission–fusion lifestyle, whereas their socioecology differs. We assessed how the occurrence of female-resisted and voluntary copulations was affected by female reproductive state, male morph (unflanged or flanged), measures of male–male competition, male–female relationship and ecological factors. Besides female reproductive state and male morph, predictors of female resistance were related to male–male competition. First, female resistance was more likely towards subordinate males who were displaced from proximity to the female by another male during that association. Second, the presence of additional flanged males increased the probability of female resistance. Third, the latency to both the arrival of another male and to the end of the association after sexual interactions was shorter if there was female resistance. We conclude that sexual coercion in orang-utans is highly dependent on the vicinity of more dominant males and can only be understood in the light of sexual conflict: While males force copulations when at risk of losing access to a female and thus follow a ‘now-or-never’ strategy, female resistance follows a ‘not-you-now’ pattern, which is ultimately consistent with an infanticide avoidance strategy.
The evolution of sexually selected traits is a major topic in evolutionary biology. However, large-scale evolutionary patterns in these traits remain understudied, especially those traits used in ...male-male competition (weapons sensu lato). Here, we analyze weapon evolution in chamaeleonid lizards, both within and between the sexes. Chameleons are an outstanding model system because of their morphological diversity (including 11 weapon types among ~220 species) and a large-scale time-calibrated phylogeny. We analyze these 11 traits among 165 species using phylogenetic methods, addressing many questions for the first time in any group. We find that all 11 weapons have each evolved multiple times and that weapon origins are generally more frequent than their losses. We find that almost all weapons have each persisted for >30 million years (and some for >65 million years). Across chameleon phylogeny, we identify both hotspots for weapon evolution (10 types present per species) and coldspots (all weapons absent, many through loss). These hotspots are significantly associated with larger male body size, but are only weakly related to sexual-size dimorphism. We also find that weapon evolution is strongly correlated between males and females. Overall, these results provide a baseline for understanding large-scale patterns of weapon evolution within clades.
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