Predatory behaviour and parental care in Argyrodes flavipes, a social spider from Queensland

Maternal Provisioning of Alkaloid Defenses are Present in Obligate but not Facultative Egg Feeding Dendrobatids

Poison frogs sequester alkaloid defenses from a diet of largely mites and ants. As a result, frogs are defended against certain predators and microbial infections. Frogs in the genus Oophaga exhibit complex maternal care, wherein mothers transport recently hatched tadpoles to nursery pools and return regularly to supply developing tadpoles with unfertilized (nutritive) eggs. Developing tadpoles are obligate egg feeders. Further, female O. pumilio and O. sylvatica maternally provision their nutritive eggs with alkaloid defenses, providing protection to their developing tadpoles at a vulnerable life-stage. In another genus of poison frog, Ranitomeya, tadpoles only receive and consume eggs facultatively, and it is currently unknown if mothers also provision these eggs (and thus their tadpoles) with alkaloid defenses. Here, we provide evidence that mother frogs of another species in the genus Oophaga (Oophaga granulifera) also provision alkaloid defenses to their tadpoles. We also provide evidence that Ranitomeya imitator and R. variabilis eggs and tadpoles do not contain alkaloids, suggesting that mother frogs in this genus do not provision alkaloid defenses to their offspring. Our findings suggest that among dendrobatid poison frogs, maternal provisioning of alkaloids may be restricted to the obligate egg-feeding members of Oophaga.

Predictors of colony extinction vary by habitat type in social spiders

Many animal societies are susceptible to mass mortality events and collapse. Elucidating how environmental pressures determine patterns of collapse is important for understanding how such societies function and evolve. Using the social spider Stegodyphus dumicola, we investigated the environmental drivers of colony extinction along two precipitation gradients across southern Africa, using the Namib and Kalahari deserts versus wetter savanna habitats to the north and east. We deployed experimental colonies (n = 242) along two ~ 800-km transects and returned to assess colony success in the field after 2 months. Specifically, we noted colony extinction events after the 2-month duration and collected environmental data on the correlates of those extinction events (e.g., evidence of ant attacks, no. of prey captured). We found that colony extinction events at desert sites were more frequently associated with attacks by predatory ants as compared with savanna sites, while colony extinctions in wetter savannas sites were more tightly associated with fungal outbreaks. Our findings support the hypothesis that environments vary in the selection pressures that they impose on social organisms, which may explain why different social phenotypes are often favored in each habitat.

Maternal care and subsocial behaviour in spiders

While most spiders are solitary and opportunistically cannibalistic, a variety of social organisations has evolved in a minority of spider species. One form of social organisation is subsociality, in which siblings remain together with their parent for some period of time but disperse prior to independent reproduction. We review the literature on subsocial and maternal behaviour in spiders to highlight areas in which subsocial spiders have informed our understanding of social evolution and to identify promising areas of future research. We show that subsocial behaviour has evolved independently at least 18 times in spiders, across a wide phylogenetic distribution. Subsocial behaviour is diverse in terms of the form of care provided by the mother, the duration of care and sibling association, the degree of interaction and cooperation among siblings, and the use of vibratory and chemical communication. Subsocial spiders are useful model organisms to study various topics in ecology, such as kin recognition and the evolution of cheating and its impact on societies. Further, why social behaviour evolved in some lineages and not others is currently a topic of debate in behavioural ecology, and we argue that spiders offer an opportunity to untangle the ecological causes of parental care, which forms the basis of many other animal societies.

The influence of vibratory courtship on female mating behaviour in orb-web spiders (Argiope keyserlingi, Karsch 1878)

Web-building spiders are important models for sexual selection. While our understanding of post-copulatory mechanisms including sperm competition and cryptic female choice is considerable, our knowledge of courtship and how it influences male and female mating decisions is still extremely poor. Here, we provide the first comprehensive description of male courtship behaviour and vibrations generated in the web by the orb-web spider, Argiope keyserlingi – a recognised model species. We identified three main elements of male courtship: shudders, abdominal wags and mating thread dances (including both plucks and bounces). The vibrations generated by these behaviours are described in detail. Male shuddering behaviour appears to have a strong influence on female latency to mate acceptance, with males that shudder at high rates without compromising shudder duration being preferred. Shuddering behaviour may also mediate female aggressive behaviour, with males that generate long shudders less likely to be cannibalised after copulation. Male abdominal wagging behaviour, however, appears to have only limited influence on female mating decisions. This study provides avenues for future work that synthesises pre- and post-copulatory mechanisms in web-building spiders to generate an all-encompassing model of how sexual selection operates.

From a comb to a tree: phylogenetic relationships of the comb-footed spiders (Araneae, Theridiidae) inferred from nuclear and mitochondrial genes

The family Theridiidae is one of the most diverse assemblages of spiders, from both a morphological and ecological point of view. The family includes some of the very few cases of sociality reported in spiders, in addition to bizarre foraging behaviors such as kleptoparasitism and araneophagy, and highly diverse web architecture. Theridiids are one of the seven largest families in the Araneae, with about 2200 species described. However, this species diversity is currently grouped in half the number of genera described for other spider families of similar species richness. Recent cladistic analyses of morphological data have provided an undeniable advance in identifying the closest relatives of the theridiids as well as establishing the family's monophyly. Nevertheless, the comb-footed spiders remain an assemblage of poorly defined genera, among which hypothesized relationships have yet to be examined thoroughly. Providing a robust cladistic structure for the Theridiidae is an essential step towards the clarification of the taxonomy of the group and the interpretation of the evolution of the diverse traits found in the family. Here we present results of a molecular phylogenetic analysis of a broad taxonomic sample of the family (40 taxa in 33 of the 79 currently recognized genera) and representatives of nine additional araneoid families, using approximately 2.5kb corresponding to fragments of three nuclear genes (Histone 3, 18SrDNA, and 28SrDNA) and two mitochondrial genes (16SrDNA and CoI). Several methods for incorporating indel information into the phylogenetic analysis are explored, and partition support for the different clades and sensitivity of the results to different assumptions of the analysis are examined as well. Our results marginally support theridiid monophyly, although the phylogenetic structure of the outgroup is unstable and largely contradicts current phylogenetic hypotheses based on morphological data. Several groups of theridiids receive strong support in most of the analyses: latrodectines, argyrodines, hadrotarsines, a revised version of spintharines and two clades including all theridiids without trace of a colulus and those without colular setae. However, the interrelationships of these clades are sensitive to data perturbations and changes in the analysis assumptions.

Competitive foraging in the social spider Stegodyphus dumicola

Reproductive skew models have greatly enhanced the study of sociality but are applicable only to societies where the aim of the members of the group is to reproduce. In 'foraging societies', where the aim of the members of the group is to grow, quite different parameters will govern the form that the societies take. We examined factors that influence the structure of foraging groups in the social spider Stegodyphus dumicola (Eresidae). In particular, we examined food distribution and consumption within groups, and how this related to predictions derived from two models. One model indicates that colonies in which individuals compete for resources via interference competition are more likely to survive than those in which individuals divide resources using scramble competition. The second model predicts the proportions of hunters, cheaters and scavengers expected in foraging groups. We found that food was not distributed evenly among group members, and that spiders that fed primarily on the head and thorax of the prey during the middle of a feeding event gained the most body mass. Spiders even lost mass if they fed only in the last hour of a foraging event. Large spiders had a competitive advantage (via interference competition) in obtaining preferred positions, and could ingest food faster than small spiders. Distributing food among colony members in this manner could cause large size differences between colony members, as predicted by the models. The implications of competitive foraging for sociality are discussed. Copyright 1999 The Association for the Study of Animal Behaviour.