Evolution of social inbreeding mating systems.

The evolution of sociality is spiders in intriguing because it involves a transition from outbreeding to inbreeding mating systems. In contrast, most cooperative animals maintain outbreeding mating systems. Inbreeding is expected to cause fitness loss (inbreeding depression). Therefore, benefits of group living such as increased survival should balance the costs associated with inbreeding. I use social and pre-social spiders of the genus Stegodyphus to investigate the costs and benefits involved in the transition from outbred to inbred social systems. The main approach is to compare mating systems, dispersal and demography; to evaluate costs and benefits of group living in field experiments; and to investigate population structure with genetic markers. I perform field work in Israel, South Africa and Namibia.

Left: Colonies of the social spider Stegodyphus dumicola (Eresidae) in Namibia, December 2003. The dense silk nests may contain several hundred spiders and are often interconnected with prey capture webs. Right: Individuals of the social spider Stegodyphus dumicola (Eresidae) foraging on a grasshopper. South Africa, January 2001.

Social spider research Namibia 2002-2004.

Evolution of Cooperation.

Kin selection theory predicts that cooperation among individuals is favoured when relatedness within groups increases. The evolution of cooperation in spiders may therefore be favoured by kin selection which compensates for costs caused by low genetic variation. I study the effect of genetic relatedness on cooperation experimentally.

Young of the subsocial spider Stegodyphus lineatus (Eresidae) consume the female 2 weeks after hatching. The suicidal maternal care by the female increases the survival chance of the young and may be a pre-condition for cooperation among siblings prior to dispersal.

Evolution of mating systems.

Females of many species mate with several males (polyandry) The evolution of polyandry is currently debated and especially interesting in species where males do not convey material benefits to the female or the offspring. In addition to the absence of direct benefits via mating, females in many spider species suffer costs through mating but are nevertheless polyandrous. I use invertebrate model systems to study the evolution of female multiple mating systems in the context of 1) Sexual conflict: Female multiple mating result form conflicting interests between males and females over mating rate; 2) Inbreeding avoidance: multiple mating serve as a counterstrategy to the risk of inbreeding, allowing females to mate with males that differ genetically and increase the genetic variation of offspring; 3) Genetic incompatibility: multiple mating provides females with the opportunity to avoid using sperm form genetically incompatible males. I perform experimental studies quantifying life history traits and genetic studies with the use of molecular markers (microsatellites and DNA fingerprinting) to identify costs or benefits of female multiple mating.

Copulation in Stegodyphus lineatus spiders (Eresidae) with the characteristic mating position of the male positioned under the female.

Evolution of mating systems in relation to social structure.

Female multiple mating may evolve to reduce the risk of inbreeding. I investigate the relationship between level of inbreeding (population structure) and degree of polyandry (natural mating rate) in the field. I investigate the following hypotheses: 1) Positive relationship between the number of mates and genetic variation of offspring. 2) Social species that experience high levels of inbreeding should show higher levels of polyandry than their pre-social and outbreeding ancestors. 3) Post-mating mechanisms that reduce relative paternity of unrelated males should be present. I perform comparative studies of mating systems in natural populations of solitary and social closely related spider species. Natural mating rated are investigated with microsatellite markers.

 

Studies on the mating system of the subsocial spider Stegodyphus lineatus (Eresidae) are done in its natural habitat in the Negev Desert, Israel. Nest and capture web of the spider are found on shrubs or thorny bushes.

Sexual selection.

I investigate the evolution of nuptial gifts in Pisaura spiders, with particular focus on sensory exploitation, sexual cannibalism avoidance and mating effort hypotheses. Females mate multiply, and I am developing microsatellite markers for Pisaura spiders to investigate models of sperm precedence in multiply mated females.

Pisaura mirabilis males offers the female a nuptial prey gift during courtship. The male holds the gift in his chelicerae and offers it to the female (right in picture). Foto: Allan Lau

 

Copulation in Pisaura mirabilis . The female consumes the nuptial gift while the male transfer sperm with his pedipalps. Foto: Allan Lau