Morphometric relationships and reproductive maturation of the mudskipper,Periophthalmus barbarus from subsistence catches in the mangrove swamps of IMO estuary,Nigeria

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Form and nature of precopulatory sexual selection in both sexes of a moth

Sexual selection is a process that operates through intrasexual competition and intersexual choice for reproduction in both sexes. Here, we report our work on a polygamous moth, Ephestia kuehniella Zeller (Lepidoptera: Pyralidae), aiming to infer the form and nature of precopulatory sexual selection in males and females. We show that, although a number of traits measured in each sex are correlated with mating success, the primary selection trait in females appears to be abdominal thickness and that in males is aedeagus length. As the female’s abdominal thickness is a reliable signal about the number and developmental stage of eggs, males who select females with thicker abdomens for mating will gain reproductive benefit, i.e., fertilizing more mature eggs. For females, earlier maturation of their eggs makes the females more likely to achieve mating earlier in an uncertain world where there is no guarantee that they will find more males in the future. Sexual selection appears to be the important force behind the evolution of fast egg maturation in females. We show that, under a male-biased sex ratio, more than 20% of mating fails within a few minutes after the aedeagus has penetrated into the female’s genitalia, suggesting that females can assess the features of the male aedeagus before allowing insemination to occur. Dissection and examination of both sexes suggest that a longer aedeagus enhances mating and fertilization efficiency in this species, supporting the notion that sexual selection is a primary force in the evolution of genital variance.     

Do females pay attention to secondary sexual coloration in vervet monkeys (Chlorocebus aethiops)?

Several primate species show sexual dichromatism with males displaying conspicuous coloration of the pelage or skin. Studies of scrotal coloration in male vervet monkeys (Chlorocebus aethiops) suggest that it is an important intrasexual signal, with relatively dark, colourful males dominating paler males. To date, no studies have examined the influence of male colour on intersexual social interactions in vervet monkeys. The primary goal of the present study was to evaluate whether female vervet monkeys attend to male coloration. We experimentally introduced females, housed with either “pale” or “dark” males, to stimulus males whose scrota were pale, dark, or pale but painted to look dark. Overall, during introductions, females did not differ in time spent directing affiliative behaviour toward pale, dark, and painted males; however, females, permanently housed with dark males, spent significantly more time directing affiliative behaviour toward pale than painted males. When the stimulus male was pale, affiliative exchanges between males and females were longer than when the stimulus male was painted. Home male colour was not related to female-initiated aggression. Home male colour was also not related to male-initiated aggression, although painted stimulus males were more likely to initiate aggression than pale stimulus males. These findings lead us to conclude that females pay attention to male coloration, but do not bias their interactions toward males solely on the basis of natural male coloration.     

Sex-dependent immune response in a semelparous spider

Previous studies on arthropods showed that seasonality and parity in breeding considerably impact the direction of sex differences in immunocompetence, and it has been suggested that life span and the time window available for breeding play key roles in shaping sex-differences in immunity. One proposed mechanism behind this phenomenon is differential investment into life history traits in sexes. Here, we tested whether in a seasonally breeding semelparous arthropod sexes differ in their immunocompetence, predicting that females would show weaker immune response than males. We compared encapsulation efficiency (a well-established and widely used method for assessing immunocompetence) of freshly matured, virgin males and females of the lycosid spider Pardosa agrestis (Westring, 1861). On average, males mounted stronger immune response than females and the extent of encapsulation was positively associated with prosoma length in males, but not in females. Also, time until maturation was positively related to the extent of encapsulation in both sexes, but did not significantly affect adult prosoma length. We propose that sex-difference in encapsulation is likely shaped by combined effects of relatively higher costs of reproduction in females, narrow time window of reproductive activity, and the absence of trade-off between current and future reproduction.     

Monogamy in a new species of wild guinea pigs (Galea sp.)

A new species of wild guinea pigs from Bolivia was recently discovered: Galea sp. So far no data are available concerning its social and mating systems. We therefore investigated behavioural compatibility, sexual dimorphism, paternity in a male-competing situation, testicular and epididymal size, and sperm morphology and motility. The results showed a complete intrasexual and moderate intersexual behavioural incompatibility between unfamiliar animals, a reversed sexual dimorphism with females larger than males, and litters always fathered by single males. Furthermore, both the reproductive organ weights and the percentage of motile sperm and sperm with intact acrosomes were significantly lower compared with the promiscuous congeneric Galea musteloides. In summary, these data strongly suggest a monogamous social and mating system for the recently discovered Galea sp.     

Sex- and age-related differences in the timing and body condition of migrating Reed Warblers Acrocephalus scirpaceus and Sedge Warblers Acrocephalus schoenobaenus

The migration strategies of birds may vary strongly between species and also between age and/or sex groups. We studied the autumn migration and body condition of molecularly sexed Reed Warblers Acrocephalus scirpaceus and Sedge Warblers Acrocephalus schoenobaenus (211 and 208 ind., respectively) at a stopover site on Lake Druzno, Northern Poland, in 2008. Immature male Reed Warblers were caught significantly later than females (median dates 9 days later), but in the Sedge Warbler, both sexes of immatures migrated at about the same time. Adult males and females of both species did not differ in their time of migration. Adult and immature males of both species were larger (wing length and body mass) than females. In both species, fat reserves were similar in both sexes of both age classes. Adults of both sexes of Reed and Sedge Warbler were generally caught earlier than immatures. In both species, the body mass and fat reserves of immatures were generally less than in adults. The autumn protogyny of immature Reed Warblers may allow smaller females to limit competition with bigger males during migration and at the wintering grounds. In the Sedge Warbler, which tends to match its migration to peak of occurrence of superabundant food at stopover sites, both sexes gain an advantage from migrating at the same time. Since part of the measured wing length variation in both species was explained by sex differences, temporal trends in wing length recorded at stopover sites should be interpreted with caution.     

接种丛枝菌根真菌对雌雄美洲黑杨吸收铅镉的影响

以雌雄美洲黑杨(Populus deltoides)为研究对象,砂培条件下,研究接种丛枝菌根真菌(Glomus intraradices)对受Pb污染(200 mg·kg-1)、Cd污染(10 mg·kg-1)及复合污染的雌雄美洲黑杨Pb和Cd的富集与分配特征的影响,关注Pb/Cd复合污染独特的环境效应.结果表明:1未接种丛枝菌根真菌条件下,与单一污染相比,复合污染增加了美洲黑杨雄株叶、粗根、细根Pb和Cd含量;复合污染增加了雌株叶片中Pb和Cd含量,却降低了粗根和细根中Pb和Cd含量;复合污染条件下雄株Pb和Cd向地上部分器官的迁移率分别增加135%和78%,雌株则分别增加52%和18%.2复合污染条件下,接种丛枝菌根真菌引起雄株Pb和Cd富集系数分别增加87%和6%,雌株则分别增加171%和65%;雄株Pb和Cd向地上部分器官的迁移率降低65%和69%,雌株则分别降低59%和53%.3Pb污染条件下,接种丛枝菌根真菌的雌雄之间Pb积累量没有显著差异;Cd污染条件下,接种丛枝菌根真菌的雄株总Cd积累量是雌株的1.7倍;复合污染条件下,接种丛枝菌根真菌的雌株Pb和Cd总积累量分别是雄株的1.3和1.2倍.本研究表明,接种G.intraradices能提高美洲黑杨的Pb和Cd积累能力,对于不同污染条件下,应根据实际情况选择合适的杨树性别进行造林和生态修复.     

Interannual differences in the relative timing of southward migration of male and female western sandpipers (Calidris mauri)

In the shorebird subfamily Calidridinae, one of the parents shortens parental care and initiates southward migration before the other. We estimated the difference in passage date between male and female western sandpipers (Calidris mauri) at their first major stopover on the southward migration from breeding areas in Alaska, in 18 years between 1978 and 2000. Overall, adult females preceded adult males by 1.22 days. A novel finding was that among juveniles, which migrate approximately a month later than adults, females preceded males by similar magnitude (1.14 days). There was wide variation among years, however, and males actually preceded females in years with late hatch. We relate these findings to hypotheses for female-first southward migration in sandpipers.     

Sexual differences in food preferences in the white stork: an experimental study

Sex differences in the foraging ecology of monomorphic species are poorly understood, due to problems with gender identification in field studies. In the current study, we used experimental conditions to investigate the food preferences of the white stork Ciconia ciconia, an opportunistic species in terms of food, but characterised by a low level of sexual dimorphism. During a 10-day experiment, 29 individuals (20 females and 9 males) were studied by means of a ‘cafeteria test’ in which the storks’ diet consisted of mammals, birds, fish, amphibians, insects and earthworms. The storks preferred food characterised by high calorific and protein values such as mammals, birds and fish. Sexes differed strongly in their preferences; males preferred mammals, whereas females preferred birds. Moreover, females consumed insects and earthworms less often than males. Interestingly, males spent significantly less time foraging than females. We have demonstrated that the white stork exhibits clear sexual differences in food preferences which are mostly attributable to differences in parental duties, physiology and anatomy.     

Predicted taxonomic patterns in pheromone production by longhorned beetles

Males of five species of three tribes in the longhorned beetle subfamily Cerambycinae produce volatile pheromones that share a structural motif (hydroxyl or carbonyl groups at carbons two and three in straight-chains of six, eight, or ten carbons). Pheromone gland pores are present on the prothoraces of males, but are absent in females, suggesting that male-specific gland pores could provide a convenient morphological indication that a species uses volatile pheromones. In this article, we assess the taxonomic distribution of gland pores within the Cerambycinae by examining males and females of 65 species in 24 tribes using scanning electron microscopy. Gland pores were present in males and absent in females of 49 species, but absent in both sexes of the remaining 16 species. Pores were confined to indentations in the cuticle. Among the species that had male-specific gland pores were four species already known to produce volatile compounds consistent with the structural motif. These findings support the initial assumption that gland pores are associated with the production of pheromones by males. There were apparently no taxonomic patterns in the presence of gland pores. These findings suggest that volatile pheromones play an important role in reproduction for many species of the Cerambycinae, and that the trait is evolutionarily labile.     

Sperm-depleted males influence the reproductive behaviour of conspecifics

In many insect species, sperm-depleted males (SDMs, i.e. males that have exhausted their sperm after a given number of matings) remain sexually active and continue to mate females. Here, we investigated the behavioural modifications that occur in both sexes of the parasitoid Asobara tabida Nees (Hymenoptera: Braconidae), after matings by fertile males and sperm-depleted males. We show that (i) virgin females, mated females and females mated to a SDM exhibited different behaviours and that (ii) males responded differently to females depending on whether the females had previously mated with an SDM or not. Our findings demonstrate that SDM influenced the reproductive behaviour of both males and females, especially with regard to male responsiveness and female attractiveness. These findings are discussed in the context of adaptive behaviour and fitness maximization in both males and females.     

Sexual dimorphism in immune function changes during the annual cycle in house sparrows

Difference between sexes in parasitism is a common phenomenon among birds, which may be related to differences between males and females in their investment into immune functions or as a consequence of differential exposure to parasites. Because life-history strategies change sex specifically during the annual cycle, immunological responses of the host aiming to reduce the impact of parasites may be sexually dimorphic. Despite the great complexity of the immune system, studies on immunoecology generally characterise the immune status through a few variables, often overlooking potentially important seasonal and gender effects. However, because of the differences in physiological and defence mechanisms among different arms of the immune system, we expect divergent responses of immune components to environmental seasonality. In male and female house sparrows (Passer domesticus), we measured the major components of the immune system (innate, acquired, cellular and humoral) during four important life-history stages across the year: (1) mating, (2) breeding, (3) moulting and (4) during the winter capture and also following introduction to captivity in aviary. Different individuals were sampled from the same population during the four life cycle stages. We found that three out of eight immune variables showed a significant life cycle stage × sex interaction. The difference in immune response between the sexes was significant in five immune variables during the mating stage, when females had consistently stronger immune function than males, while variables varied generally non-significantly with sex during the remaining three life cycle stages. Our results show that the immune system is highly variable between life cycle stages and sexes, highlighting the potential fine tuning of the immune system to specific physiological states and environmental conditions.     

Female reciprocal calling in the Iberian midwife toad (Alytes cisternasii) varies with male call rate and dominant frequency: implications for sexual selection

Male midwife toads (Alytes cisternasii) responded differently depending on the call frequency and call rate of other males. I tested female Iberian midwife toads with the same set of stimuli used earlier with males. Females responded faster to high call rates, and female vocal activity was greater in response to low-frequency male calls. Thus, in both sexes, the vocal response differs in the same direction according to signal frequency variation, but the magnitude of the response is greater in males than in females. In the light of these results, I discuss the implications for sexual selection of this reciprocal calling.     

The effect of female wings on male courtship behavior in the cricket Gryllus bimaculatus

Sexual dimorphism exists in the shape and the structure of the forewings of the cricket (Gryllus bimaculatus). However, the functional significance of the wings in the G. bimaculatus female has been unclear. In common blue butterflies (Polyommatus icarus), wings in females have been suggested as being important for attracting males. To test whether female crickets need wings for conspecific males to recognize them and initiate mating behavior, we removed all wings from females and observed the behavior of males towards them. Most males (87.5%) showed mating behavior towards the wingless females: they produced courtship song and transferred spermatophores to the wingless females. Similarly, 88.5% of the males showed mating behavior towards intact females. When males were placed with both a wingless female and an intact female, no significant difference was detected in male mate choice. The findings demonstrate that the wing of the G. bimaculatus female is not necessary for female recognition by conspecific males and the initiation of male mating behavior, and that it is not important in male mate choice.     

Differential timing and latitudinal variation in sex ratio of Aquatic Warblers during the autumn migration

Differential migration has been extensively reported in spring, but less so in autumn, particularly in relation to sex in monomorphic bird species. Here, we analysed the autumn passage of a monomorphic, globally threatened passerine, the Aquatic Warbler Acrocephalus paludicola throughout Western Europe, with regard to age and sex. We showed that, overall, adults migrated earlier than first-year birds, and males migrated earlier than females during the autumn migration. This may be caused by an overall social dominance of adults over immatures, and differentiated migration strategy of males and females. In addition, we found male-skewed sex proportions, with a tendency to an equalised ratio in more southern stopover sites. This may indicate a male bias in the global population or different migration strategies of the sexes. Differential migration may cause the age and sex classes to be exposed differently to various threats affecting demographic structure of the species.     

Mating System and Sexual Selection in the Scorpionfly Panorpa vulgaris (Mecoptera: Panorpidae)

Panorpa vulgaris   has become a model insect for testing theories of sexual selection. This contribution summarizes that which has been learned in recent years and presents new data that clearly show that the mating system of P. vulgaris is not simply a resource-defense polygyny, as has previously been thought. In P. vulgaris neither the pattern in food exploitation nor the ratio of variance in the lifetime reproductive success of the two sexes is in accordance with that expected in resource defense polygynous mating systems. Lifetime mating duration is the most important proximate determinant of male fitness. Males employing alternative mating tactics obtain copulations of varying duration in relation to the following sequence: saliva secretion  1  food offering  1  no gift. The number of salivary masses which males provide to females during their lifetime is significantly correlated with the lifetime condition index. The condition index depends on the fighting prowess of males and their ability to find food items. Thus saliva secretion of Panorpa is considered a Zahavian handicap, which can serve as an honest quality indicator used by mating females. Our results confirm four main predictions of the indicator model of the theory of sexual selection: (a) the indicator signals high ecological quality of its bearer, (b) the indicator value increases with phenotypic quality, (c) the indicator value is positively correlated with the genetic quality affecting offspring fitness in a natural selection context, and (d) the quality indicator is more costly for low- than for high-quality individuals. The evolutionary consequences of the mating pattern and the sperm competition mechanism in P. vulgaris are discussed in the context the way in which sexual selection creates and maintains sperm mixing and the evolution of a promiscuous mating system.     

Sexually dichromatic coloration reflects size and immunocompetence in female Spanish terrapins, Mauremys leprosa

Many studies have shown the importance of colorful ornamentation in mate choosiness or intrasexual conflict. However, research on color ornaments has focused mainly on birds, lizards or fish, but remains practically unknown in other animal groups such as turtles. In addition, female ornaments and their relation with sexual selection also remain almost unknown. Here, we measured the coloration of the shell and the limb stripes of male and female Spanish terrapins Mauremys leprosa and explored the existence of sexual dichromatism and the relation of color characteristics with body size and health state estimated from the immune response to the injection of an antigen (phytohaemagglutinin test). Our results showed that shell coloration, which could be constrained by natural selection to be cryptic, changed with body size, but did not differ between sexes. In contrast, females had brighter and less ultraviolet-saturated and more orange-saturated limb stripes than males. In females, interindividual variation in limb stripe coloration was related with body size and immune response suggesting that this coloration may inform honestly about multiple traits that could be important in sexual selection. In contrast, coloration of limb stripes of males was duller than in females, and was not related with any trait suggesting that coloration is not important in sexual selection for males.     

Trophic attributes of the mudskipper,Periophthalmus barbarus (Gobiidae: Oxudercinae) in the mangrove swamps of Imo River Estuary,Nigeria

Aspects of the trophic attributes of the mudskipper, Periophthalmus barbarus occurring in the mangrove swamps of Imo River　Estuary, Nigeria, were investigated during a 12-month period (April, 1992-March, 1993). Feeding intensity increased with size, it was　higher in the dry season(November-April) than in the wet season(May-October), monthly changes in the indices of feeding intensity were　significantly correlated. Major food objects comprised detritus and benthic algae; crustaceans, insects, macrophyte matter and sand grains were minor food objects while fish, molluscs, Chilopoda, nematodes and fungi were unconsciously devoured objects. Diet varied seasonally; algae and sesarmid crabs were generally more in the dry season than during the rains whereas FPOM and fish increased in the wet over dry season.The mudskipper display a high degree of euryphagy and can be considered as a generalist and an omnivore. The lower trophic status of P.barbarus qualifies it as a good aquaculture candidate. Food richness was higher in big-sized class(BSC) than small-sized class(SSC). Sizebased and seasonal variations were not apparent in food richness. Diet breadth was higher in the BSC than the SSC, there was dry season increase in diet breadth.     

Anatomic and acoustic sexual dimorphism in the sound emission system of Phoenicoprocta capistrata (Lepidoptera: Arctiidae)

Both sexes of Phoenicoprocta capistrata have functional tymbals. The scanning electron microscopy revealed differences in the morphology of these organs in males and females. Male tymbals have a well-developed striated band, constituted by 21 ± 2 regularly arranged striae whereas female tymbals lack a striated band. This type of sexual dimorphism is rare in Arctiidae. The recording of the sound produced by moths held by the wings revealed that while males produced trains of pulses organized in modulation cycles, females produced clicks at low repetition rate following very irregular patterns. Statistically, there are differences between sexes in terms of the duration of pulses, which were 355 ± 24 μs in the case of males and 289 ± 29 μs for females. The spectral characteristics of the pulses also show sexual dimorphism. Male pulses are more tuned (Q ₁₀ = 5.2 ± 0.5) than female pulses (Q ₁₀ = 2.7 ± 0.5) and have a higher best frequency (42 ± 1 kHz vs. 29 ± 2 kHz). To our knowledge, this is the first report on an arctiid moth showing sexual dimorphism in tymbal’s anatomy that leads to a best frequency dimorphism. Males produce sound at mating attempts. The sounds recorded during mating are modulation cycles with the same spectral characteristics as those recorded when males are held by the wings. The morphological and acoustic features of female tymbals could indicate a process of degeneration and adaptation to conditions under which the emission of complex patterns is not necessary. Frank Coro no longer works at Universidad de La Habana.     

An equal sex ratio followed by differential sex mortality causes overestimation of females in gall midges: no evidence for sex ratio regulation

Monogeny, the production of unisexual broods by individual females, has been recognized for nearly 80?years. The genetic nature of gall midges' sex determination predicts an equal numbers of male-producing and female-producing females in the populations such that the overall sex ratio is expected to be nearly 1:1. However, observations of some strictly monogenous populations with biased sex ratio, mainly toward females, have raised the question of whether gall midges are able to adjust their offspring sex ratio in response to changes in environmental conditions, and some authors have even considered sex ratio regulation as a strong force in the course of the evolution of monogeny. In this paper, first, by studying the sex ratio variations of the predatory gall midge, Aphidoletes aphidimyza within a generation, we showed that adult males emerge up to 1?day earlier and have shorter life span than females (less than 4?days and up to 6?days, respectively). Although, the sex ratio of A. aphidimyza at the time of emergence was nearly 1:1 (52.41?% males), a simple population simulation indicated that the differential mortality of sexes can lead to a female-biased sex ratio estimation (57.88?% females) under random sampling in the natural environments. Our results imply that the primary sex ratio of monogenous gall midges is nearly 1:1 and that the arrhenogenic/thelygenic gall midges are not able to alter the number of their male/female progenies in response to changes in environmental conditions.