Female common lizards (Lacerta vivipara) do not adjust their sex-biased investment in relation to the adult sex ratio

Sex allocation theory predicts that facultative maternal investment in the rare sex should be favoured by natural selection when breeders experience predictable variation in adult sex ratios (ASRs). We found significant spatial and predictable interannual changes in local ASRs within a natural population of the common lizard where the mean ASR is female-biased, thus validating the key assumptions of adaptive sex ratio models. We tested for facultative maternal investment in the rare sex during and after an experimental perturbation of the ASR by creating populations with female-biased or male-biased ASR. Mothers did not adjust their clutch sex ratio during or after the ASR perturbation, but produced sons with a higher body condition in male-biased populations. However, this differential sex allocation did not result in growth or survival differences in offspring. Our results thus contradict the predictions of adaptive models and challenge the idea that facultative investment in the rare sex might be a mechanism regulating the population sex ratio.     

Observations on the sexual system and the natural history of the semi-terrestrial shrimp Merguia rhizophorae (Rathbun, 1900)

Abstract. The sexual system of the semi-terrestrial shrimp Merguia rhizophorae is described, along with natural history observations on this unusual caridean. Individuals of M. rhizophorae in the Bocas del Toro Archipelago, Panama, were found occupying fossilized coral terraces in the upper and mid-intertidal zones, inhabiting caves and crevices, in and out of water. These fossilized coral terraces represent a new habitat for this species, which was previously reported only from mangrove swamps. Males, which made up 65% of the studied population, were smaller than females on average. No small juvenile females were observed, but transitional individuals having the characteristics of both males (gonopores) and females (ovaries) were observed in the population. These data suggest that individuals of M. rhizophorae are protandric hermaphrodites. Logistic regression indicated that the carapace length at which 50% of the individuals change sex is 4.89 mm. The abundance of shrimps at the study site was low. Shrimps were usually solitary, but occasionally observed in groups of ≤5 individuals. Shrimps were commonly observed walking while out of water, and in some cases, emerged shrimps jumped vigorously, presumably to avoid capture by the researcher or by predatory crabs. Additional studies on the reproductive biology and the behavioral ecology of members of this genus and of members of the closely related families Barbouridae and Lysmatidae will aid in understanding the evolutionary origin and the adaptive value of gender expression patterns in shrimps.     

Relation between the outer cover of the egg case of Argiope aurantia (Araneae: Araneidae) and the emergence of its spiderlings

To emerge from the egg case, Argiope aurantia spiderlings must penetrate a tightly woven outer cover composed primarily of large-diameter cylindrical gland fibers and small-diameter fibers, likely of aciniform gland origin. They accomplish this using enzymatic digestion and mastication to form a communal hole in the outer cover. The involvement of proteolytic enzymes in this process was demonstrated by zymography of spiderling homogenates and washes made from the edges of holes. The specific source(s) of the proteases is unknown, but histological examination of spiderling sections indicates that the digestive tract, venom glands, and gnathocoxal glands are all functioning at the time of emergence from the egg case. Observations on edges of holes indicate that spiderlings are able to solubilize the small-diameter fibers completely, but cylindrical gland fibers only partially. In the outer cover, cylindrical fibers are composed of numerous fibrils embedded within a matrix. Spiderlings appear to be unable to solubilize the fibrils, but digestion of the matrix allows the spiderlings to push the fibrils aside to create the opening.     

Phylogeny of the orb-weaving spider family Araneidae (Araneae: Araneoidea)

We present a new phylogeny of the spider family Araneidae based on five genes (28S, 18S, COI, H3 and 16S) for 158 taxa, identified and mainly sequenced by us. This includes 25 outgroups and 133 araneid ingroups representing the subfamilies Zygiellinae Simon, 1929, Nephilinae Simon, 1894, and the typical araneids, here informally named the “ARA Clade”. The araneid genera analysed here include roughly 90% of all currently named araneid species. The ARA Clade is the primary focus of this analysis. In taxonomic terms, outgroups comprise 22 genera and 11 families, and the ingroup comprises three Zygiellinae and four Nephilinae genera, and 85 ARA Clade genera (ten new). Within the ARA Clade, we recognize ten informal groups that contain at least three genera each and are supported under Bayesian posterior probabilities (≥ 0.95): “Caerostrines” (Caerostris, Gnolus and Testudinaria), “Micrathenines” (Acacesia, Micrathena, Ocrepeira, Scoloderus and Verrucosa), “Eriophorines” (Acanthepeira, Alpaida, Eriophora, Parawixia and Wagneriana), “Backobourkiines” (Acroaspis, Backobourkia, Carepalxis, Novakiella, Parawixia, Plebs, Singa and three new genera), “Argiopines” (Arachnura, Acusilas, Argiope, Cyrtophora, Gea, Lariniaria and Mecynogea), “Cyrtarachnines” (Aranoethra, Cyrtarachne, Paraplectana, Pasilobus and Poecilopachys), “Mastophorines” (Celaenia, Exechocentrus and Mastophora,), “Nuctenines” (Larinia, Larinioides and Nuctenea), “Zealaraneines” (Colaranea, Cryptaranea, Paralarinia, Zealaranea and two new genera) and “Gasteracanthines” (Augusta, Acrosomoides, Austracantha, Gasteracantha, Isoxya, Macracantha, Madacantha, Parmatergus and Thelacantha). Few of these groups are currently corroborated by morphology, behaviour, natural history or biogeography. We also include the large genus Araneus, along with Aculepeira, Agalenatea, Anepsion, Araniella, Cercidia, Chorizopes, Cyclosa, Dolophones, Eriovixia, Eustala, Gibbaranea, Hingstepeira, Hypognatha, Kaira, Larinia, Mangora, Metazygia, Metepeira, Neoscona, Paraplectanoides, Perilla, Poltys, Pycnacantha, Spilasma and Telaprocera, but the placement of these genera was generally ambiguous, except for Paraplectanoides, which is strongly supported as sister to traditional Nephilinae. Araneus, Argiope, Eriophora and Larinia are polyphyletic, Araneus implying nine new taxa of genus rank, and Eriophora and Larinia two each. In Araneus and Eriophora, polyphyly was usually due to north temperate generic concepts being used as dumping grounds for species from southern hemisphere regions, e.g. South-East Asia, Australia or New Zealand. Although Araneidae is one of the better studied spider families, too little natural history and/or morphological data are available across these terminals to draw any strong evolutionary conclusions. However, the classical orb web is reconstructed as plesiomorphic for Araneidae, with a single loss in “cyrtarachnines”–“mastophorines”. Web decorations (collectively known as stabilimenta) evolved perhaps five times. Sexual dimorphism generally results from female body size increase with few exceptions; dimorphic taxa are not monophyletic and revert to monomorphism in a few cases.     

A phylogenetic analysis of the orb-weaving spider family Araneidae (Arachnida, Araneae)

We present the first cladistic analysis focused at the tribal and subfamily level of the orb-weaving spider family Araneidae. The data matrix of 82 characters scored for 57 arancid genera of 6 subfamilies and 19 tribes (and 13 genera from 8 outgroup families) resulted in 16 slightly different, most parsimonious trees. Successive weighting corroborated 62 of the 66 informative nodes on these cladograms; one is recommended as the 'working' araneid phylogcny. The sister group of Araneidae is all other Araneoidea. Araneidae comprises two major clades: the subfamily Araneinae, and the 'argiopoid' clade, which includes all other subfamilies and most tribes (((Gasteracanthinae, Caerostreae), (((Micratheninae, Xylcthreae), Eruyosaccus ), (Eurycorminae, Arciinae)), Cyrlarachninae), ((Argiopinae, Cyrtophorinae), Arachnureae)). Cyrtarachneae and Mastophoreae are united in a new subfamily, Cyr-tarachninae. The spiny orb-weavers alone (Gasteracanthinae and Micratheninae) are not monophyletic. The mimetid subfamily Arciinae and the 'tetragnathid' genus Zygiella are araneids, but .Nephila (and other tetragnathids) are not. On the preferred tree, web decorations (stabilimenta) evolved 9 times within 15 genera, and were lost once. The use of silk to subdue prey evolved once in cribellate and four times in ecribillate orb weavers. Sexual size dimorphism evolved once in nephilines, twice in araneids, and reverted to monomorphism five times. Evolution in other genitalic and somatic characters is also assessed; behavioral and spinneret features arc most consistent (male genitalia, leg and prosomal features least consistent) on the phylogeny.     

Previous experience and site tenacity in the orb spider Nephila (Araneae,Araneidae)

Summary The tenacity of the orb spider Nephila clavipes to a web site was studied in the laboratory. No differences were found between the giving-up-times and the site tenacity of spiders reared in the laboratory or those caught in the field, nor between spiders raised under a poor or a richt diet. The animals left sites at random and seemed to ignore experiences gained at previous sites.     

Maternal investment in a spider with suicidal maternal care, Stegodyphus lineatus (Araneae, Eresidae)

Providing parental care is costly for the parent, but generally beneficial for the young whose survival, growth and reproductive value can be increased. Selection should strongly favour an optimal distribution of parental resources, depending on the relationship between the costs and benefits for parents and their offspring. Parental care is characterized by trade offs in investment, for example between egg size and number of young or providing resources at the egg stage versus the post-hatching stage. Females of the spider Stegodyphus lineatus (Eresidae) produce a single small brood with small eggs and provide the young with regurgitated fluid and later, with their body contents via matriphagy. We asked whether females adjust the investment of resources differentially into eggs, regurgitation feeding and matriphagy, and how maternal investment affects the size of the young at dispersal. We followed the growth of young of broods in the lab and in the field and manipulated brood size in order to determine the pattern of resource allocation. We found that brood size was positively correlated with body mass: larger females had larger broods. Females provided 95% of their body mass to the young, allocating more resources to regurgitation than to matriphagy. Females provided regurgitated food to the young according to the brood size, providing less food when the brood was reduced. Maternal resources had a large influence on offspring mass at dispersal, which is likely to affect their future fitness. The study shows the importance of the female's body mass and her resource allocation decisions for her reproductive outcome.     

Intranidal mating,emergence, and sex ratio in a communal beeAndrena jacobi Perkins 1921 (Hymenoptera: Andrenidae)

The extent of preemergence intranidal mating, schedules of emergence, and sex ratio at emergence were documented forAndrena jacobi, a communal, univoltine bee, by collecting and dissecting adults as they emerged from their fossorial nests in 1994. Over 70% of females had mated intranidally with nestmate males, thus potentially incestuously, before emerging. Preemergence intranidal mating did not vary during a day or between nests within a day, though it was less frequent at the start and end of the period of emergence. It was independent of a female's size.A. jacobi was protandrous, though some males emerged after all females. The sex ratio at emergence was remarkably female biased, possibly a consequence of local mate competition. Intranidal mating may represent a characteristic trait of communal bees where a high density of receptive females are predictably aggregated within a nest.     

雄全同株植物簇花芹花期性别分配与开花式样

簇花芹(Soranthus meyeri)是古尔班通古特沙漠中常见的、具雄全同株性系统的伞形科多年生早春短命植物。该文对簇花芹花期性比(两性花数/总花数)与植株大小的关系及其开花式样进行了研究, 重点对花期大小依赖的性别资源分配进行了讨论。结果表明: 2006-2008年簇花芹群体水平的性比分别为0.69 ± 0.03、0.62 ± 0.03和0.69 ± 0.02, 彼此间无显著差异( p > 0.05), 表明其性比是相对稳定的, 可能受遗传因素的控制。雄花生物量与花粉量均比两性花的小, 说明产生雄花比产生两性花所需资源少。一级复伞形花序比二级复伞形花序具有较多的两性花, 说明前者易从植株上获得资源用于增加雌性适合度; 而后者产生较多的雄花以避免在雌性功能上资源投入的浪费, 增大花展示以吸引更多传粉者来增加花粉输出总量, 提高其整体适合度。植株水平的性比与地上营养器官的生物量间呈正相关关系, 说明较大个体对雌性功能的投资较大, 雌性繁殖成功受资源限制。复伞形花序内各伞形花序几乎同时向心开放, 且所有两性花及花序均为雄性先熟, 雌雄阶段完全分离, 但一级复伞形花序比二级复伞形花序早开放约5天, 彼此开花重叠期约为1天。这些特征对于一级复伞形花序进行异株异花授粉以及植株内不同级别花序间的同株异花传粉、避免雌雄功能间的干扰具有重要意义。     

Male emergence timing and mating success in the funnel-web spider,Agelena limbata (Araneae: Agelenidae)

Field observations on the relationship between male mating success and emergence timing in the funnel-web spider,Agelena limbata, were conducted.Agelena limbata is an annual species and adult males appear slightly earlier than adult females in July. As males deposit a copulatory plug at the female epigynum after copulation, copulation with virgin females is important to males. The number of copulations in males with virgin females, which strongly correlates with the longevity of males and the number of females that males courted, did not correlate with the emergence timing of males. Early emerged males and females were significantly larger in size than later ones, but the correlation coefficient between the emerged date and the cephalothorax width was not strong. Males that emerged earlier did not have any advantage in copulating with larger and more fecund females. Furthermore, virgin females first copulated on average 7.9 days after their final molt and the mortality rate of adult males increased after the final molt. These factors may favor the smaller degree of protandry in male emergence timing inA. limbata.     

Extraordinary web and silk properties of Cyrtarachne (Araneae, Araneidae): a possible link between orb-webs and bolas

Cyrtarachne is an orb-weaving spider of the sub-family Cyrtarachninae (Araneidae), which includes the triangle-web-building Pasilobus and the bolas spiders. We found that web and thread characteristics of Cyrtarachne differed greatly from those of typical orb-webs. Web diameter, sticky spiral spacing, breaking strength and stickiness of thread, thread diameter and droplet diameter were significantly different from those of other members of Araneidae. It is especially worth noting that the diameter was approximately four times, and the breaking strength seven to ten times larger in Cyrtarachne viscid threads than in those of other araneids. Kinetic energy-absorbing ability of Cyrtarachne threads was much greater than in that of other species, and close to the amount of kinetic energy generated by flying moths. Viscid material of threads was peculiar because its adhesiveness decreased to zero in a few hours. Moreover, SEM photos revealed them to be covered with thin scales of material, while threads of other araneids were smooth. These two facts suggest that the viscid material of Cyrtarachne threads may be different from those of other orb-weavers. As web-building, hunting behaviour and prey composition of different species of Cyrtarachninae arc quite similar to each other, we hypothesize that these extraordinary web and thread characteristics of Cyrtarachne are shared by the other members of this sub-family. Because these characteristics differ in many ways from those of typical araneid orb-webs, there appears to have been a great leap in evolution between Cyrtarachne and the other Araneidae.     

Heterozygosity and fitness in a California population of the labyrinth spider Metepeira ventura (Araneae, Araneidae)

Abstract. The relationship between individual heterozygosity and characteristics likely to be associated with fitness was investigated in the labyrinth spider Metepeira ventura . Adult females and their egg sacs were collected at a coastal site in southern California, and three measures of bodily condition (carapace width, weight, residual index) and six measures of reproductive output (number of egg sacs, variation in egg number among sacs [coefficient of variation], total number of eggs, mean eggs/sac, mean eggs/sac divided by carapace width, mean eggs/sac divided by weight) were determined for each spider. The sample was polymorphic at three allozyme loci that were in Hardy–Weinberg equilibrium, and individual females were heterozygous at up to two of the three loci, forming three heterozygosity classes (0, 1, and 2). None of the bodily condition measures were significantly related to the number of heterozygous loci, while four of the reproductive output estimators (total number of eggs, mean eggs/sac, mean eggs/sac divided by carapace width, mean eggs/sac divided by weight) were significantly influenced by heterozygosity. In each significant case, values for class 2 females were less than those for class 0 and 1 females, whose values were usually more similar. Thus, while female bodily condition was comparable among classes, the most heterozygous females produced fewer total eggs and eggs per sac than their less heterozygous peers. The fact that females of M. ventura engage in a reproductive investment-number trade-off suggests that high-variability and low-variability females may be pursuing distinct reproductive strategies in the wild, with more heterozygous females being K -selected (smaller clutches, heavier eggs) and more homozygous females being r -selected (larger clutches, lighter eggs). Further investigation will be needed to assess more fully the fitness value of heterozygosity in M. ventura .     

Function of bright coloration in the wasp spider Argiope bruennichi (Araneae: Araneidae)

There are two major competing explanations for the counter-intuitive presence of bright coloration in certain orb-web spiders. Bright coloration could lure insect prey to the web vicinity, increasing the spider's foraging success. Alternatively, the markings could function as disruptive camouflage, making it difficult for the insect prey to distinguish spiders from background colour variation. We measured the prey capture rates of wasp spiders, Argiope bruennichi, that were blacked out, shielded from view using a leaf fragment, or left naturally coloured. Naturally coloured spiders caught over twice the number of prey as did either blacked-out or leaf-shielded spiders, and almost three times as many orthopteran prey. Spectrophotometer measurements suggest that the bright yellow bands on the spider's abdomen are visible to insect prey, but not the banding on the legs, which could disguise the spider's outline. Thus, our results provide strong support for the hypothesis that bright coloration in the wasp spider acts as a visual lure for insect prey and weak support for the hypothesis that the arrangement of the banding pattern across the spider's body disguises the presence of the spider on the web.     

Seasonal sex ratio and unbalanced investment sex ratio in the Banksia bee Hylaeus alcyoneus

Abstract 1. Hylaeus alcyoneus is an endemic solitary bee common on coastal heaths of Western Australia. The bee is unusual in that males are larger than females. This size dimorphism presents an opportunity to test the theory of resource-dependent sex allocation, in which theory predicts that when resources are low the sex ratio should be biased towards the smaller sex. In most bees, females are larger than males and, in line with theoretical prediction, sex ratios are male biased when resources are scarce.
2. The emerging sex ratio and brood mass from a natural population of H. alcyoneus using trap nests was studied over two seasons (1999, 2000). A switch from a male- to a female-biased sex ratio through the season was found, which was related to a reduced floral resource.
3. Fisherian sex ratio theory predicts that total investment in each sex throughout a season should be equal and that the sex ratio should be biased towards the smaller sex. By measuring the mass of the emerging progeny, the total investment was found to favour males. Possible explanations for this bias in investment are discussed.     

Organization of the spinnerets and spigots in the orb web spider,Argiope bruennichi (Araneae: Araneidae)

Although the basic taxonomic characteristics usually remain unchanged, some spinning apparatuses undergo consistent adaptive variations. As the presence of additional protuberances known as nubbins and tartipores have caused disagreements regarding some Araneidae spiders, more detailed definitions on the cuticular structures have recently been proposed. Reflecting this definition, microstructural organization of silk spinning apparatuses in the orb web spider Argiope bruennichi were reconsidered using field emission scanning electron microscopy. Among the seven kinds of functional spigots in females, it was revealed that two types (major ampullates and pyrifoms) are located on anterior spinnerets and another five types are distributed on median (minor ampullates, tubuliforms and aciniforms) or posterior (tubuliforms, flagelliforms, aggregates and aciniforms) spinnerets, respectively. In addition to functional spigots, cuticular remnants of the nubbins and the tartipores were found on the spinning fields, but the number of tartipores on each spinneret varied among individuals based on maturity. Nevertheless, three kinds of cuticular protuberances of ampullate silk glands were clearly visible at both the anterior and median spinnerets.     

A new combination expands the range of the African araneid spider Singafrotypa (Araneae, Araneidae)

Study of the syntype of Larinioides subinermis, a species known from Ethiopia only, revealed that it actually belongs to Singafrotypa Benoit, 1962. We redescribe Singafrotypa subinermis (Caporiacco, 1940), comb. n., and provide a key to females of four species belonging to Singafrotypa. A distribution map for all species is provided.     

Ecology of a bolas spider,Mastophora hutchinsoni: phenology,hunting tactics,and evidence for aggressive chemical mimicry

Summary Bolas spiders are relatively rare members of the large family known as orb weavers. Instead of using a typical web to capture prey, late-stadia and adult female bolas spiders swing a droplet of adhesive on a thread at flying insects. Mastophora hutchinsoni (Araneae: Araneidae) is one of five Mastophora species known from the United States and occurs over much of eastern North America. It is univoltine in Kentucky and overwinters in the egg stage. Spiderling emerged in May, the diminutive males matured in late June and early July, and females matured in early September. Eggs were produced from late September to late October or early November. This report is the first complete documentation of the population phenology of any bolas spider. Newly-emerged M. hutchinsoni spiderlings did not use a bolas, but instead hunted by positioning themselves on the underside of leaf margins where they ambushed small arthropods that crawled along the leaf margins. Subadult and adult female M. hutchinsoni used a bolas to capture moths. Only male moths were captured, specifically three species of Noctuidae (bristly cutworm, bronzed cutworm, and smoky tetanolita) and one species of Pyralidae (bluegrass webworm). Among 492 prey captured by more than twenty spiders at two sites during 1985 and 1986, smoky tetanolita moths and bristly cutworm moths accounted for 93% of the total. The flight behavior of approaching moths, the limited taxa caught from a large available moth fauna, and the fact that only males were caught support the hypothesis that the spider attracts its prey by producing chemicals which mimic the sex pheromones of these moth species. Adult female M. hutchinsoni frequently captured more than one moth species on a given night. The two most common prey species were active at different times of night, the bristly cutworm soon after nightfall and the smoky tetanolita generally between 11:00 p.m. and dawn. This pattern suggests that mating activity of these moth species may be temporally isolated, a common phenomenon when sympatric species have similar pheromones. If so, the spider could capture both species without producing different pheromone-mimicking compounds, simply by hunting during the activity period of each species.The investigation reported in this paper (No. 87-7-76) is in connection with a project of the Kentucky Agricultural Experiment Station and is published with the approval of the Director     

Genital damage in the orb-web spider Argiope bruennichi (Araneae: Araneidae) increases paternity success

The morphology of male genitalia often suggests functions besidessperm transfer that may have evolved under natural or sexualselection. In several species of sexually cannibalistic spiders,males damage their paired genitalia during mating, limitingthem to one copulation per pedipalp. Using a triple-mating experiment,we tested if genital damage in the orb-web spider Argiope bruennichiincreases male fitness either through facilitating his escapefrom an aggressive female or by obstructing the female's inseminationducts against future copulation attempts from other males. Wefound no survival advantage for males damaging their pedipalps;however, copulations into a previously used insemination ductwere significantly shorter when the previous male had left partsof his genitalia inside the insemination duct. Because copulationduration determines paternity in this species, our result suggeststhat male genital damage in A. bruennichi is sexually selected.By breaking off parts of their intromittent organs inside avirgin female, males can reduce sperm competition and therebyincrease their paternity success.     

Colony structure, provisioning and sex allocation in the sweat bee Halictus ligatus (Hymenoptera: Halictidae)

Population and colony-level sex allocation and nest productivity in the eusocial sweat bee Halictus ligatus Say were studied by excavating nests during one season. The emphasis was on measuring the provision masses, which differ in size and shape depending on the sex of the egg to be laid on them (male-producing provision masses are smaller and more or less round, whereas gyne-producing provision masses are larger and 'loaf-shaped). The primary aim of this study was to test theoretical predictions about female-bias of the sex ratio in the summer brood, both on the population level and on the colony level.
The overall sex ratio of the summer brood was moderately biased towards gynes. A significant positive correlation between the overall size of provision masses (as an estimate for the degree of female bias of the nest sex ratio) and the number of eusocial workers was found. This relationship further improved in partial analyses in which the provision mass weights were adjusted for sampling date, removing the effect of protandry. Foundress size, however, had no effect on the second brood provision masses and neither was there an effect of worker number on the size of gynes and males separately. In the first brood only the size of the foundress had a consistently positive effect on the size of the provision masses and on the size of the emerging daughter workers.
The observed increase of female bias in the nest sex ratio with increasing numbers of eusocial worker bees conforms to optimization predictions following from kin-selection theory.