Homing in the wolf spider Lycosa tarantula (Araneae, Lycosidae): the role of active locomotion and visual landmarks

Previous studies on the homing of the wolf spider Lycosa tarantula have shown that it is carried out by path integration. Animals using this mechanism must measure the distance walked and the angles turned. This study aims to understand if wolf spider L. tarantula is able to estimate the walked distance in an outward path. As this information is more likely obtained by proprioceptive mechanisms, active or passive displacements have been performed. An active locomotion was found essential to estimate distances. During passive locomotion, spiders searched for their burrows near the release point while when displaced actively the inbound journey was longer than the outbound one. The possible use of visual landmarks near the burrow was also tested as a cue to complete the inbound journey. Our results did not show that L. tarantula used these visual landmarks to find the burrow. L. tarantula seems to use only proprioceptive information obtained during the outbound path to estimate the distance traveled.     

Nutritional correlates and mate acquisition role of multiple sexual traits in male collared flycatchers

The information content of a sexual signal may predict its importance in a multiple signal system. Many studies have correlated sexual signal expression with the absolute levels of nutrient reserves. In contrast, the changes of nutrient reserves associated with signal expression are largely unknown in the wild due to technical limitations although they are important determinants of signal information content. We compared two visual and eight acoustic sexual traits in male collared flycatchers to see whether the nutritional correlates of expression predict the role of the signal in sexual selection. We used single point assays of plasma lipid metabolites to estimate short-term changes in nutritional state in relation to sexual trait expression during courtship. As a measure of sexual selection, we estimated the relationship with pairing latency after arrival in a 4-year dataset. Males which found a mate rapidly were characterized by large wing and forehead patches, but small song strophe complexity and small figure repertoire size. Traits more strongly related to pairing latency were also more closely related to changes in nutrient reserves. This indicates a link between signal role and information content. Small wing patches and, surprisingly, complex songs seemed to indicate poor phenotypic quality and were apparently disfavoured at mate acquisition in our population. Future studies of the information content of sexual traits, especially dynamic traits such as song, may benefit from the use of plasma metabolite profiles as non-invasive indicators of short-term changes in body condition.     

Behavioural evidence of male volatile pheromones in the sex-role reversed wolf spiders Allocosa brasiliensis and Allocosa alticeps

The use of chemical signals in a sexual context is widespread in the animal kingdom. Most studies in spiders report the use of female pheromones that attract potential sexual partners. Allocosa brasiliensis and Allocosa alticeps are two burrowing wolf spiders that show sex-role reversal. Females locate male burrows and initiate courtship before males perform any detectable visual or vibratory signal. So, females of these species would be detecting chemical or mechanical cues left by males. Our objective was to explore the potential for male pheromones to play a role in mate detection in A. brasiliensis and A. alticeps. We designed two experiments. In Experiment 1, we tested the occurrence of male contact pheromones by evaluating female courtship when exposed to empty burrows constructed by males or females (control). In Experiment 2, we tested the existence of male volatile pheromones by evaluating female behaviour when exposed to artificial burrows connected to tubes containing males, females or empty tubes (control). Our results suggest the occurrence of male volatile pheromones that trigger female courtship in both Allocosa species. The sex-role reversal postulated for these wolf spiders could be driving the consequent reversal in typical pheromone-emitter and detector roles expected for spiders.     

Geographical variation in parasitism shapes larval immune function in a phytophagous insect

Two of the central goals of immunoecology are to understand natural variation in the immune system among populations and to identify those selection pressures that shape immune traits. Maintenance of the immune system can be costly, and both food quality and parasitism selection pressure are factors potentially driving immunocompetence. In tritrophic interactions involving phytophagous insects, host plants, and natural enemies, the immunocompetence of phytophagous insects is constrained by selective forces from both the host plants and the natural enemies. Here, we assessed the roles of host plants and natural enemies as selective pressures on immune variation among natural populations of Lobesia botrana. Our results showed marked geographical variation in immune defenses and parasitism among different natural populations. Larval immune functions were dependent of the host plant quality and were positively correlated to parasitism, suggesting that parasitoids select for greater investment into immunity in moth. Furthermore, investment in immune defense was negatively correlated with body size, suggesting that it is metabolically expensive. The findings emphasize the roles of host plants and parasitoids as selective forces shaping host immune functions in natural conditions. We argue that kinds of study are central to understanding natural variations in immune functions, and the selective forces beyond.     

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.     

Cross-habitat variation in the phenology of a colonial spider: insights from a reciprocal transplant study

In species with widespread distribution, populations found in markedly different environments can show differences in developmental traits. This, in time, can have an effect on reproductive success. Sources of variation in developmental traits can be genetic or environmentally induced. I examined the relationship between environmental and genetic influences on juvenile development in populations of the colonial spider, Parawixia bistriata, located at sites with different moisture regimes and associated environmental variables (e.g., prey availability). It was expected that individuals from different populations would show differences in developmental traits and that those differences will be associated with lower reproductive success at dry sites. I recorded the phenology and developmental traits of native and transplanted individuals in the field and estimated reproductive success based on clutch size. Colonies from wet versus dry sites showed different phenologies, with individuals at dry sites maturing later. Transplant results suggest plasticity in instar duration caused by environmental effects. Despite differences in resources and spider phenology, clutch sizes of native dry and wet populations were similar. Transplanted individuals, however, were differentially affected. Transplants from wet to dry sites (WD) showed lower growth rates and smaller clutches, whereas transplants from dry to wet sites had larger clutch sizes than in native habitat. Delayed maturation and failure to reproduce in WD individuals is associated with a lower tendency to capture prey in groups and less aggressive interactions during prey capture. Thus, despite negative environmental effects on development, dry native individuals have evolved non-developmental traits that allow successful reproduction.     

Copulatory behavior in a pholcid spider: males use specialized genitalic movements for sperm removal and copulatory courtship

Sexual selection may operate on pre-copulatory, copulatory, and post-copulatory traits. An example of a copulatory target of sexual selection is the genitalic movements a male performs during copulation. These movements may function either to prevent sperm competition or to influence a female’s fertilization decision. Here we investigated how copulation duration, pedipalp movements, and abdominal movements that males of the pholcid spider Holocnemus pluchei produce during copulation influence sperm removal and/or patterns of successful sperm transfer. We compared mating events with virgin and mated females for differences in copulatory and post-copulatory behavior. We expected longer copulation duration, longer pedipalp movement duration, and more complex and frequent pedipalp and abdominal movements when males mated with mated females compared to virgin females. Except for abdominal movements, our results corroborated these predictions. Furthermore, when we investigated mating events with mated females, we observed sperm mass ejection from the female gonopore and physical removal of sperm by males’ procursi. Females with interrupted second mating events showed a significant reduction of stored sperm masses compared to females with completed mating events. We suggest that males use alternating pedipalp movements to remove most of the rival sperm stored by mated females prior to sperm transfer. Copulation duration and pedipalp movements can be further used to transfer sperm and/or as a form of genitalic copulatory courtship.     

Aggressive behavior of the male parent predicts brood sex ratio in a songbird

Brood sex ratio is often affected by parental or environmental quality, presumably in an adaptive manner that is the sex that confers higher fitness benefits to the mother is overproduced. So far, studies on the role of parental quality have focused on parental morphology and attractiveness. However, another aspect, the partner’s behavioral characteristics, may also be expected to play a role in brood sex ratio adjustment. To test this hypothesis, we investigated whether the proportion of sons in the brood is predicted by the level of territorial aggression displayed by the father, in the collared flycatcher (Ficedula albicollis). The proportion of sons in the brood was higher in early broods and increased with paternal tarsus length. When controlling for breeding date and body size, we found a higher proportion of sons in the brood of less aggressive fathers. Male nestlings are more sensitive to the rearing environment, and the behavior of courting males may often be used by females to assess their future parental activity. Therefore, adjusting brood sex ratio to the level of male aggression could be adaptive. Our results indicate that the behavior of the partner could indeed be a significant determinant in brood sex ratio adjustment, which should not be overlooked in future studies.     

Maternally derived carotenoid pigments affect offspring survival, sex ratio, and sexual attractiveness in a colorful songbird

In egg-laying animals, mothers can influence the development of their offspring via the suite of biochemicals they incorporate into the nourishing yolk (e.g. lipids, hormones). However, the long-lasting fitness consequences of this early nutritional environment have often proved elusive. Here, we show that the colorful carotenoid pigments that female zebra finches (Taeniopygia guttata) deposit into egg yolks influence embryonic and nestling survival, the sex ratio of fledged offspring, and the eventual ornamental coloration displayed by their offspring as adults. Mothers experimentally supplemented with dietary carotenoids prior to egg-laying incorporated more carotenoids into eggs, which, due to the antioxidant activity of carotenoids, rendered their embryos less susceptible to free-radical attack during development. These eggs were subsequently more likely to hatch, fledge offspring, produce more sons than daughters, and produce sons who exhibited more brightly colored carotenoid-based beak pigmentation. Provisioned mothers also acquired more colorful beaks, which directly predicted levels of carotenoids found in eggs, thus indicating that these pigments may function not only as physiological ‘damage-protectants’ in adults and offspring but also as morphological signals of maternal reproductive capabilities.     

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.     

Integrated plumage colour variation in relation to body condition, reproductive investment and laying date in the collared flycatcher

The possible integration of different sexual ornaments into a composite system, and especially the information content of such ornament complexes, is poorly investigated. Many bird species display complex plumage coloration, but whether this represents one integrated or several independent sexual traits can be unclear. Collared flycatchers (Ficedula albicollis) display melanised and depigmented plumage areas, and the spectral features (brightness and UV chroma) of these are correlated with each other across the plumage. In a 5-year dataset of male and female plumage reflectance, we examined some of the potential information content of integrated, plumage-level colour attributes by estimating their relationships to previous and current year body condition, laying date and clutch size. Females were in better condition the year before they became darker pigmented, and males in better current year condition were also darker pigmented. Female pigment-based brightness was positively, while male structurally based brightness was negatively related to current laying date. Finally, the overall UV chroma of white plumage areas in males was positively associated with current clutch size. Our results show that higher degree of pigmentation is related to better condition, while the structural colour component is associated with some aspects of reproductive investment. These results highlight the possibility that correlated aspects of a multiple plumage ornamentation system may reflect together some aspects of individual quality, thereby functioning as a composite signal.     

Nested patterns in hyporheic meta-communities: the role of body morphology and penetrability of sediment

Nestedness has been regarded as a common pattern of species distribution especially in terrestrial systems and vertebrate faunas. However, a significantly lower degree of nestedness has been reported for aquatic invertebrates. We analyzed the vertical distribution patterns of taxa in the upper 70 cm of the hyporheic zone. This biotope is abundantly inhabited by epigean fauna, which is morphologically pre-adapted to life within the limited space of sediment interstices. We tested the hypotheses that in the vertical profile of the hyporheic zone sediment acts as a physical barrier (filter), allowing only the morphologically pre-adapted and adapted (i.e., smaller, narrower, more flexible) taxa to penetrate to deeper layers. We demonstrated that this mechanism can promote a strongly nested and colonization-driven pattern at higher taxa levels. The sediment filter (1) constricted the body width: 0.50 mm appeared to be the upper limit for successful sediment colonization at the study site, and (2) favored elongated taxa against small sized taxa. We tested also the assumption that distribution of fine sediment affects the accessibility of hyporheic zone for fauna (“filter density”) and thereby influences nestedness. However, we found that nestedness could be sufficiently explained by the depth itself. Our study offers a possible explanation of depth patterns in hyporeic meta-communities as a result of morphological characteristics promoting nestedness at higher taxa level.     

Ethanol concentration in food and body condition affect foraging behavior in Egyptian fruit bats (Rousettus aegyptiacus)

Ethanol occurs in fleshy fruit as a result of sugar fermentation by both microorganisms and the plant itself; its concentration [EtOH] increases as fruit ripens. At low concentrations, ethanol is a nutrient, whereas at high concentrations, it is toxic. We hypothesized that the effects of ethanol on the foraging behavior of frugivorous vertebrates depend on its concentration in food and the body condition of the forager. We predicted that ethanol stimulates food consumption when its concentration is similar to that found in ripe fruit, whereas [EtOH] below or above that of ripe fruit has either no effect, or else deters foragers, respectively. Moreover, we expected that the amount of food ingested on a particular day of feeding influences the toxic effects of ethanol on a forager, and consequently shapes its feeding decisions on the following day. We therefore predicted that for a food-restricted forager, ethanol-rich food is of lower value than ethanol-free food. We used Egyptian fruit bats (Rousettus aegyptiacus) as a model to test our hypotheses, and found that ethanol did not increase the value of food for the bats. High [EtOH] reduced the value of food for well-fed bats. However, for food-restricted bats, there was no difference between the value of ethanol-rich and ethanol-free food. Thus, microorganisms, via their production of ethanol, may affect the patterns of feeding of seed-dispersing frugivores. However, these patterns could be modified by the body condition of the animals because they might trade-off the costs of intoxication against the value of nutrients acquired.     

大气挥发性有机物的日变化特征及在臭氧生成中的作用——以广州夏季为例

为了得到实时的大气挥发性有机物(VOCs)浓度组成和日变化特征,2006年夏季在广州市区内高约55m的楼顶采用在线的气相色谱仪进行了为期一个月的观测.结果表明,影响城市VOC含量的物种以及对臭氧生成有重要贡献的典型物种的日变化存在不同的特征.烷烃类和烯烃类物种出现早晚高峰值,估计主要与机动车排放有关,芳香烃除了与交通排放有关,还受到溶剂挥发的影响,早晨的峰值晚于交通高峰时间.异戊二烯在正午时间出现一天的单峰值,主要来自于天然源排放.乙苯和间对二甲苯的比值被用来表征采样点上气团光化学反应的进程,通常情况下,广州市区点气团经历的光化学进程越久,臭氧浓度越高.     

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.