Ecological correlates in the evolution of moult strategies in Western Palearctic passerines

Moult is an important process in the life cycle of birds. Passerines differ widely in the number, seasonality and extension of moult episodes, but the incidence of birds ecology on this variation remains largely uninvestigated. We analysed the patterns of moult in European passerines in relation to their distribution, migration and sexual dichromatism. Longer migrations and southern wintering quarters were characteristic of species with complete moults in summer and an additional moult in winter. The main moult in species with larger seasonal changes in sexual dimorphism tended to be scheduled just before the start of the breeding season, suggesting a link between sexual selection and the timing of moult. These patterns strongly support the importance of migration and dichromatism on the evolution of moult strategies.     

Fecundity,reproductive effort,and pupal size in the profundal midgeChironomus cuccini (Diptera: Chironomidae)

Fecundity ofChironomus cucini increased linearly across a three-fold range of female pupal biomass. Females from a lake producing small pupae (Crystal Lake) had an average of 303 primary follicles, while larger pupae from Trout Lake had an average fecundity of 582. Pupae produced in Crystal Lake from larvae that received experimental food supplements were intermediate in size and fecundity. Pupal biomass explained 76% of the variation in fecundity. No difference in egg size was detected between pupae from the two lakes, and an average value of 2.1 g egg^–1 was used to calculate the total biomass allocated to eggs in each of 79 females dissected. This measure of reproductive effort scaled isometrically with pupal mass. On average, females allocated 48% of their biomass to eggs and 52% to somatic tissues. A comparison of average male biomass to female somatic biomass across 12 populations indicated that the biomass difference between the sexes is a biased predictor of fecundity.     

Sexual dimorphism and allometry of external morphology in Oreochromis mossambicus

Sexual dimorphism in growth of conventional morphometric characters was investigated in juveniles and young adults (size range: 31 to 91 mm) of Oreochromis mossambicus . A closely associated set of traits was identified that shows sexually dimorphic growth, which was positively allometric in the males. These traits correspond to two different morphological complexes: jaw structure and anal/dorsal fins. The best sex discriminators among this set of traits were premaxilla width, anal fin height and snout length. These findings may be explained in terms of intra– and inter–sexual selection acting together and favouring males with strong and large mouths and high dorsal and anal fins, traits that are important in agonistic displays (jaw and fins), fighting and nest digging (jaw).     

Relative growth before and after sexual maturity in Ocypode platytarsis (Milne Edwards) and Ocypode cordimana (Desmarest) (Crustacea: Decapoda)

The relative growth of two species of the genus Ocypode inhabiting different ecological niches was studied before and after sexual maturity. The growth coefficient of both sexes of O. cordimana, which inhabits supra-littoral zones, is higher than that of O. platytarsis found in wave-wash zones.s

Some characteristics such as eyestalk length, major chela width and obdomen width do not show any difference in the growth pattern of either species of Ocypode at the onset of sexual maturity. Other characteristics such as minor and major chela length in male O. platytarsis; carapace length, minor chela length and width in female O. platytarsis; major chela length and third walking leg length in male O. cordimana showed a difference in the growth pattern after the onset of sexual maturity.

Major chela length of males of both species is clearly a sexually dimorphic feature since it showed an increase in the growth coefficient after sexual maturity. Merus length in male O. platytarsis and minor chela length in female O. cordimana also showed such sexual dimorphism.

There are several characteristics in which the growth coefficient declines after sexual maturity. The change in growth coefficient of different characteristics may depend on the adaptive value of the characteristic in reproductive or post-reproductive activities of O. cordimana and O. platytarsis.     

Function and evolution of the frill of the frillneck lizard, Chlamydosaurus kingii (Sauria: Agamidae)

Relative to body size, the frill of the Australian agamid lizard Chlamydosaurus kingii is one of the largest and most spectacular display structures seen in any animal species. More than 300 hours observation of free-ranging lizards, combined with data on museum specimens, revealed that the frill is used primarily for intraspecific communication and predator deterrence. Earlier hypotheses on alternative uses for the frill (gliding, food storage, thermoregulation or auditory enhancement) are not supported. The folded frill may also enhance camouflage, but this is probably a fortuitous effect rather than an adaptation.
Male frillnecks frequently display and fight during the mating season. Male displays are highly stereotyped, and involve repeated partial erection of the frill, head-bobbing, tail-lashing, and waving of forelimbs. Both males and females erect the frill during social encounters, and in response to potential predators. Males grow larger than females and have larger heads than do females at the same body size, but no dimorphism is apparent in the relative size of the frill. The extreme development of the display structure in this species may be due to general allometric relationships, as well as to ecological features that have intensified the action of sexual selection in Chlamydosaurus.     

Macroevolutionary patterns of sexual size dimorphism in copepods

Major theories compete to explain the macroevolutionary trends observed in sexual size dimorphism (SSD) in animals. Quantitative genetic theory suggests that the sex under historically stronger directional selection will exhibit greater interspecific variance in size, with covariation between allometric slopes (male to female size) and the strength of SSD across clades. Rensch''s rule (RR) also suggests a correlation, but one in which males are always the more size variant sex. Examining free-living pelagic and parasitic Copepoda, we test these competing predictions. Females are commonly the larger sex in copepod species. Comparing clades that vary by four orders of magnitude in their degree of dimorphism, we show that isometry is widespread. As such we find no support for either RR or for covariation between allometry and SSD. Our results suggest that selection on both sexes has been equally important. We next test the prediction that variation in the degree of SSD is related to the adult sex ratio. As males become relatively less abundant, it has been hypothesized that this will lead to a reduction in both inter-male competition and male size. However, the lack of such a correlation across diverse free-living pelagic families of copepods provides no support for this hypothesis. By comparison, in sea lice of the family Caligidae, there is some qualitative support of the hypothesis, males may suffer elevated mortality when they leave the host and rove for sedentary females, and their female-biased SSD is greater than in many free-living families. However, other parasitic copepods which do not appear to have obvious differences in sex-based mate searching risks also show similar or even more extreme SSD, therefore suggesting other factors can drive the observed extremes.     

Sexual dimorphism in chelicerae size in three species of nuptial-gift spiders: a discussion of possible functions and driving selective forces

Positive allometric patterns observed for intersexual signalling characters are related to directional sexual selection, and supported by theoretical and empirical data. Recent models have shown that positive allometry may not hold as a rule if the influence of natural selection is added to the model. Here we tested these models applying traditional morphometrical techniques for the analysis of chelicerae sexual dimorphism and allometric patterns within the genus Paratrechalea : Paratrechalea azul , Paratrechalea galianoae and Paratrechalea ornata . Spider chelicerae are basically used for prey capture, but males of Paratrechalea also use the chelicerae to offer a nuptial gift during courtship, also presenting a clear size and colour sexual dimorphism supporting a possible role as a signal. Chelicerae size was male biased for all the variables studied and showed an isometric pattern, while females showed a higher variation. Our findings are in accordance with models of viability-related function for prey capture, questioning some statements proposed by the positive allometry model.     

Is diversification in male reproductive traits driven by evolutionary trade-offs between weapons and nuptial gifts?

Many male animals have evolved exaggerated traits that they use in combat with rival males to gain access to females and secure their reproductive success. But some male animals invest in nuptial gifts that gains them access to females. Both these reproductive strategies are costly in that resources are needed to produce the weapon or nuptial gift. In closely related species where both weapons and nuptial gifts are present, little is known about the potential evolutionary trade-off faced by males that have these traits. In this study, we use dobsonflies (order Megaloptera, family Corydalidae, subfamily Corydalinae) to examine the presence and absence of enlarged male weapons versus nuptial gifts within and among species. Many dobsonfly species are sexually dimorphic, and males possess extremely enlarged mandibles that they use in battles, whereas in other species, males produce large nuptial gifts that increase female fecundity. In our study, we show that male accessory gland size strongly correlates with nuptial gift size and that when male weapons are large, nuptial gifts are small and vice versa. We mapped weapons and nuptial gifts onto a phylogeny we constructed of 57 species of dobsonflies. Our among-species comparison shows that large nuptial gift production evolved in many species of dobsonfly but is absent from those with exaggerated weapons. This pattern supports the potential explanation that the trade-off in resource allocation between weapons and nuptial gifts is important in driving the diversity of male mating strategies seen in the dobsonflies, whereas reduced male–male competition in the species producing large spermatophores could be an alternative explanation on their loss of male weapons. Our results shed new light on the evolutionary interplay of multiple sexually selected traits in animals.