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.     

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.     

Differential sex- and age-related migration of Bluethroats Luscinia svecica at Eilat, Israel

This paper examines the phenology and biometrics of Bluethroats staging in the Eilat region. This is of special interest because of the extreme conditions with which this temperate zone breeding species has to contend because Eilat is a desert habitat and is the last green area before the crossing of the deserts in autumn or after it in spring. Data were collected during 20 spring and 18 autumn migration seasons in the years 1984–2003, and a total of 7,464 Bluethroat were recorded. The number of trapped birds was much higher in autumn than in spring. The majority of Bluethroats caught in both the autumn and spring migrations were juveniles. We found differences in sex ratio in the individual age classes only in the autumn wherein among both adults and juveniles, males were in greater numbers. We also found significant differences in the dates of ringed birds from different sex–age classes in the spring and in autumn migrations. In spring, males from both age classes were caught earlier than females. In autumn, adult birds arrived earlier than juveniles. We think that it is important to identify and conserve the high quality stopover habitats such as Eilat wherein not only Bluethroats have been shown to stopover but also several hundred other species.     

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.     

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.     

The fractal dimension of a conspicuous ornament varies with mating status and shows assortative mating in wild red-legged partridges (<Emphasis Type="Italic">Alectoris rufa</Emphasis>)

Complex body designs, such as plumage ornaments in birds, can be described by fractal geometry. These complex patterns could have a role as visual signals during courtship and social interactions, but an empirical validation in the wild is currently lacking. Here, we investigated whether the fractal dimension (FD) of a complex plumage pattern displayed by red-legged partridges Alectoris rufa could function as a potential sexual signal. We captured wild birds early in the breeding season and tested if mated and unmated birds differed in the FD of their conspicuous melanin-based black bib. We also tested if the FD of the black bib was correlated within the pair, looking for evidence of assortative mating based on the expression of this trait. We simultaneously assessed similar effects in other ornamental traits (black bib size, white throat patch and black flank band surface, redness of the eye rings and bill). Mated birds showed higher black bib FD values than unmated ones. Mated males, but not females, also displayed a larger black bib. Moreover, the black bib FD (but not the trait size) and the white throat patch surface showed assortative mating. Finally, females with higher black bib FD showed smaller black flank band surface, suggesting a trade-off in the expression of the two melanin-pigmented plumage traits. This provides unique and novel indication for the shape complexity of a pigmented trait, here described by its fractal dimension, to be potentially under sexual selection in a wild animal.     

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.     

Unusually high-pitched neonate distress calls of the open-habitat Mongolian gazelle (<Emphasis Type="Italic">Procapra gutturosa</Emphasis>) and their anatomical and hormonal predictors

In neonate ruminants, the acoustic structure of vocalizations may depend on sex, vocal anatomy, hormonal profiles and body mass and on environmental factors. In neonate wild-living Mongolian gazelles Procapra gutturosa, hand-captured during biomedical monitoring in the Daurian steppes at the Russian-Mongolian border, we spectrographically analysed distress calls and measured body mass of 22 individuals (6 males, 16 females). For 20 (5 male, 15 female) of these individuals, serum testosterone levels were also analysed. In addition, we measured relevant dimensions of the vocal apparatus (larynx, vocal folds, vocal tract) in one stillborn male Mongolian gazelle specimen. Neonate distress calls of either sex were high in maximum fundamental frequency (800–900 Hz), but the beginning and minimum fundamental frequencies were significantly lower in males than in females. Body mass was larger in males than in females. The levels of serum testosterone were marginally higher in males. No correlations were found between either body mass or serum testosterone values and any acoustic variable for males and females analysed together or separately. We discuss that the high-frequency calls of neonate Mongolian gazelles are more typical for closed-habitat neonate ruminants, whereas other open-habitat neonate ruminants (goitred gazelle Gazella subgutturosa, saiga antelope Saiga tatarica and reindeer Rangifer tarandus) produce low-frequency (<200 Hz) distress calls. Proximate cause for the high fundamental frequency of distress calls of neonate Mongolian gazelles is their very short, atypical vocal folds (4 mm) compared to the 7-mm vocal folds of neonate goitred gazelles, producing distress calls as low as 120 Hz.     

Sex pheromone component ratios and mating isolation among three Lygus plant bug species of North America

The plant bugs Lygus hesperus, Lygus lineolaris, and Lygus elisus (Hemiptera: Miridae) are major pests of many agricultural crops in North America. Previous studies suggested that females release a sex pheromone attractive to males. Other studies showed that males and females contain microgram amounts of (E)-4-oxo-2-hexenal, hexyl butyrate, and (E)-2-hexenyl butyrate that are emitted as a defense against predators. Using gas chromatography–mass spectrometry, we found that female L. lineolaris and L. elisus have a 4:10 ratio of hexyl butyrate to (E)-2-hexenyl butyrate that is reversed from the 10:1 ratio in female L. hesperus (males of the three species have ~10:1 ratio). These reversed ratios among females of the species suggest a behavioral role. Because both sexes have nearly equal amounts of the major volatiles, females should release more to attract males. This expectation was supported because L. hesperus females released more hexyl butyrate (mean of 86 ng/h) during the night (1800–0700 hours) than did males (<1 ng/h). We used slow-rotating pairs of traps to test the attraction of species to blends of the volatiles with a subtractive method to detect synergism. Each species’ major butyrate ester was released at 3 μg/h, the minor butyrate according to its ratio, and (E)-4-oxo-2-hexenal at 2 μg/h. The resulting catches of only Lygus males suggest that (E)-4-oxo-2-hexenal is an essential sex pheromone component for all three species, (E)-2-hexenyl butyrate is essential for L. elisus and L. lineolaris, and hexyl butyrate is essential for L. hesperus. However, all three components are recognized by each species since ratios of the butyrate esters are critical for conspecific attraction and heterospecific avoidance by males and thus play a role in reproductive isolation among the three species. Because L. hesperus males and females are known to emit these major volatiles for repelling ant predators, our study links defensive allomones in Lygus bugs with an additional use as sex pheromones.     

Habitat quality affects stress responses and survival in a bird wintering under extremely low ambient temperatures

Animals normally respond to stressful environmental stimuli by releasing glucocorticoid hormones. We investigated whether baseline corticosterone (CORT), handling-induced corticosterone concentration(s), and body condition indices of members of willow tit (Poecile montanus) groups differed while wintering in old growth forests and managed young forests in mild weather conditions and during cold spells. Willow tits spend the winter season in non-kin groups in which dominant individuals typically claim their priority to access resources, while subordinate individuals may experience greater levels of stress and higher mortality, especially during cold spells. We captured birds to measure baseline CORT and levels of handling-induced CORT secretion after 20 min of capture. Willow tits in the young forests had higher baseline CORT and a smaller increase in CORT in response to capture than individuals in the old forests. Baseline CORT was higher in females and juvenile birds compared to adult males, whereas handling-induced CORT secretion did not differ between birds of different ages. During cold spells, baseline CORT of willow tits increased and handling-induced CORT secretion decreased, especially in birds in young forests. Willow tits’ survival was higher in the old forests, with dominant individuals surviving better than subordinates. Our results show that changes in CORT secretion reflect responses to habitat quality and climate harshness, indicating young managed coniferous forests as a suboptimal habitat for the willow tit.     

辽宁滨海(环渤海)湿地鸟类多样性调查与研究

本研究于2019－2020年对辽宁滨海（环渤海）湿地开展了春迁徙季、秋迁徙季、繁殖季和越冬季的鸟类多样性调查,共监测到鸟类150种,隶属于16目38科,其中,留鸟25种,夏侯鸟26种,冬侯鸟26种,旅鸟73种;国家一级保护鸟类11种,国家二级保护鸟类20种。调查显示:调查区内鸟类多样性的季节差异明显,春、秋迁徙季,鸟类种类与数量明显高于其他两季,越冬季鸟类的种类数量均最少,丰富度指数、均匀度指数、多样性指数和优势度指数均最低。空间分布显示,盘锦地区鸟类种类和数量均最多,达到78种,473084只;营口地区调查到的鸟类种类最少,为55种;锦州地区鸟类数量最少,只有57723只。从鸟类多样性对比来看,盘锦地区最高,大连地区最低,各地鸟类群落组成的空间差异较为明显,在一定程度上受到该地区鸟类生境种类数量及面积大小的影响。辽宁滨海（环渤海）湿地作为东亚—澳大利西亚候鸟迁徙带上的关键区域,当前正面临气候变化、人类围垦干扰造成的鸟类栖息地减少等不利情况,建议通过扩大保护范围、实施修复和管理对策措施、强化宣传等手段保护鸟类多样性及其栖息生境,巩固渤海综合治理攻坚战的治理成效。     

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.     

Temporal variation in size-assortative mating and male mate choice in a spider with amphisexual care

Males should be more selective when they have a high investment in reproduction, especially in species with biparental or paternal care. In this context, male mate choice can promote size-assortative mating (SAM) when (1) large males win intrasexual disputes, (2) large females are more fecund, and (3) males prefer larger females to smaller ones. In the spider Manogea porracea, males exhibit high reproductive investment by building their webs above those of females and exhibiting extended care of offspring in the absence of females. Under these circumstances, we expect the occurrence of SAM and male preference for large females. Herein, we performed observations and experiments in the field to evaluate the hypotheses that (1) M. porracea mates assortatively by size and (2) SAM is influenced by male mate choice. Furthermore, we measured variables that could affect mating patterns, the sex ratios, and densities of both sexes. Pairing in M. porracea was positively size-assortative in 2012, but not in 2013. Large males won most disputes for mates and preferred larger females, which produced more eggs. The inconsistency in detection of SAM was due to population dynamics, namely variations in sex ratio and population density across the breeding season. Furthermore, we found that the significance of male mate choice on sexual selection of body size in M. porracea strongly depends on the competition intensity for mating opportunities. The traditional sexual selection hypothesis of SAM needs to be reviewed and must include measures of competition intensity.     

Sex-dependent obesogenic effect of tetracycline on Drosophila melanogaster deteriorated by dysrhythmia

Antibiotics have been identified as obesogens contributing to the prevalence of obesity. Moreover, their environmental toxicity shows sex dependence, which might also explain the sex-dependent obesity observed. Yet, the direct evidence for such a connection and the underlying mechanisms remain to be explored. In this study, the effects of tetracycline, which is a representative antibiotic found in both environmental and food samples, on Drosophila melanogaster were studied with consideration of both sex and circadian rhythms (represented by the eclosion rhythm). Results showed that in morning-eclosed adults, tetracycline significantly stimulated the body weight of females (AM females) at 0.1, 1.0, 10.0 and 100.0 µg/L, while tetracycline only stimulated the body weight of males (AM males) at 1.0 µg/L. In the afternoon-eclosed adults, tetracycline significantly stimulated the body weight of females (PM females) at 0.1, 1.0 and 100.0 µg/L, while it showed more significant stimulation in males (PM males) at all concentrations. Notably, the stimulation levels were the greatest in PM males among all the adults. The results showed the clear sex dependence of the obesogenic effects, which was diminished by dysrhythmia. Further biochemical assays and clustering analysis suggested that the sex- and rhythm-dependent obesogenic effects resulted from the bias toward lipogenesis against lipolysis. Moreover, they were closely related to the preference for the energy storage forms of lactate and glucose and also to the presence of excessive insulin, with the involvement of glucolipid metabolism. Such relationships indicated potential bridges between the obesogenic effects of pollutants and other diseases, e.g., cancer and diabetes.     

Male antenna morphology and its effect on scramble competition in false garden mantids

Well-developed antennae are crucial for many insects, but especially for scramble competitors, who race to find their mates using female sex cues. In these systems, the ability of males to locate females quickly is thought to be under strong selection. A rarely tested assumption is that males with more sensory structures are able to locate females faster. In the present study, we used the false garden mantid Pseudomantis albofimbriata to investigate male antennal morphology and its effect on male efficiency in finding a mate. We used scanning electron microscopy to describe the major sensilla types and their arrangement along the length of male antennae. We also conducted field enclosure trials relating male antennal morphology to scramble competition in this system. We identified six different types of antennal sensilla (cheatic, trichoid, basiconic, grooved peg, ceolocapitular and campaniform) on male P. albofimbriata antennae. As expected, males who had more trichoid sensilla located females quicker than did males with fewer sensilla. Results of the current study suggest that antenna morphology plays a significant role in mate location and hence scramble competition in the P. albofimbriata mating system.     

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.     

Sexual selection on receptor organ traits: younger females attract males with longer antennae

Sexual selection theory predicts that female choice may favour the evolution of elaborate male signals. Darwin also suggested that sexual selection can favour elaborate receiver structures in order to better detect sexual signals, an idea that has been largely ignored. We evaluated this unorthodox perspective by documenting the antennal lengths of male Uraba lugens Walker (Lepidoptera: Nolidae) moths that were attracted to experimentally manipulated emissions of female sex pheromone. Either one or two females were placed in field traps for the duration of their adult lives in order to create differences in the quantity of pheromone emissions from the traps. The mean antennal length of males attracted to field traps baited with a single female was longer than that of males attracted to traps baited with two females, a pattern consistent with Darwin’s prediction assuming the latter emits higher pheromone concentrations. Furthermore, younger females attracted males with longer antennae, which may reflect age-specific changes in pheromone emission. These field experiments provide the first direct evidence of an unappreciated role for sexual selection in the evolution of sexual dimorphism in moth antennae and raise the intriguing possibility that females select males with longer antennae through strategic emission of pheromones.     

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.     

Body size phenotypes are heritable and mediate fecundity but not fitness in the lepidopteran frugivore Cydia pomonella

The inheritance and functional roles of quantitative traits are central concerns of evolutionary ecology. We report two sets of experiments that investigated the heritability and reproductive consequences of body size phenotypes in a globally distributed lepidopteran frugivore, Cydia pomonella (L.). In our first set of experiments, we tested the hypotheses that (1) body size is heritable and (2) parental body size mediates egg production and offspring survival. Midparent–offspring regression analyses revealed that body mass is highly heritable for females and moderately heritable for males. The contribution of fathers to estimates of additive genetic variance was slightly greater than for mothers. Egg production increased with mean parental size, but offspring survival rates were equivalent. Based on this result, we tested two additional hypotheses in a second set of experiments: (3) male size moderates female egg production and egg fertility and (4) egg production, egg fertility, and offspring survival rate are influenced by female mating opportunities. Females paired with large males produced more eggs and a higher proportion of fertile eggs than females paired with small males. Females with multiple mating opportunities produced more fertile eggs than females paired with a single male. However, egg production and offspring survival rates were unaffected by the number of mating opportunities. Our experiments demonstrate that body mass is heritable in C. pomonella and that size phenotypes may mediate fecundity but not fitness. We conclude that male size can influence egg production and fertility, but female mate choice also plays a role in determining egg fertility.     

Ovarian fluid of receptive females enhances sperm velocity

The females of several internal fertilizers are able to store sperm for a long time, reducing the risk of sperm limitation. However, it also means that males can attempt to mate outside females’ receptive period, potentially increasing the level of sperm competition and exacerbating sexual conflict over mating. The guppy (Poecilia reticulata), an internally fertilizing fish, is a model system of such competition and conflict. Female guppies accept courtship and mate consensually only during receptive periods of the ovarian cycle but receive approximately one (mostly forced) mating attempt per minute both during and outside their sexually receptive phase. In addition, females can store viable sperm for months. We expected that guppy females would disfavour sperm received during their unreceptive period, possibly by modulating the quality and/or quantity of the components present in the ovarian fluid (OF) over the breeding cycle. Ovarian fluid has been shown to affect sperm velocity, a determinant of sperm competition success in this and other fishes. We found that in vitro sperm velocity is slower in OF collected from unreceptive females than in OF from receptive females. Visual stimulation with a potential partner prior to collection did not significantly affect in vitro sperm velocity. These results suggest that sperm received by unreceptive females may be disfavoured as sperm velocity likely affects the migration process and the number of sperm that reach storage sites.