Currently, 4 PhD students and about the same number of Master candidates are working on different behavioral biology topics. One of our PhD students is in a joint PhD program with Macquarie University in Sydney, Australia currently here in Hamburg. Our main study organisms are orb-web spiders of the genus Argiope and Trichonephila as well as jumping spiders like Maratus, saitis and Marpissa.
Sexual selection and mating systems in spiders
Monogynous mating systems in which males show an extremely high mating investment have evolved several times independently in spiders. Monogynous males do not provide brood care but nevertheless mate with a single female while females can be polyandrous. We are interested in the causes and consequences of such mating systems and focus on the genera Nephila and Argiope which represent two independent origins.
All Argiope species are sexually cannibalistic. Males damage their genitalia during copulation and apply broken off pieces from their pedipalps as genital plugs. Thereby males reduce the risk of sperm competition. Since both males and females have paired genitalia, males can monopolize paternity with a female by plugging both her genital openings. Females can prevent monopolisation by killing a male before he can copulate a second time. This sexual conflict raises interesting questions as for example whether males are choosy and only die for high quality mates.
In spiders we investigate mechanisms of mate choice decisions which is mostly male mate choice in sexually cannibalistic species. We already know that males use social cues from females to adjust maturation. Now we ask how males find females and which information they use to make decisions about their mating investment.
Sexual dichromatism in jumping spiders
Jumping spiders (Salticidae) are known for their diverse sexually dichromatic coloration, with males exhibiting colorful patterns on their front-facing body surfaces and engaging in dynamic visual courtship displays. The usual assumption, that female choosiness is the primary evolutionary force driving the existence of such color patterns, has recently started to crumble as more and more data show a surprising lack of choosiness in females. To better understand the evolutionary forces driving jumping spiders’ eye-catching displays, we are investigating the visual capabilities and sensory biases of jumping spiders, focusing on the extremely colorful Maratus peacock jumping spiders from Australia, as well as their closest European relatives, Saitis. One of our most important tools is a multispectral camera that allows us to visualize how jumping spiders see each other’s colors and patterns through their own eyes.
Seeing the world through animal eyes
In visual and behavioral ecology, light radiating from natural surfaces like plants and animal color patches is generally quantified using point reflectance measurements and mathematical models of diffuse reflectance. We have recently shown that such methods can sometimes be poor approximations of how light behaves when interacting with common natural objects. To better understand how animals see the world, we employ multispectral imaging with optical filters custom-made to mimic real animal spectral sensitivities. By visualizing objects directly, in situ, we preserve natural habitat lighting geometry and reduce the number of assumptions made in visual modeling. “Seeing” through animal eyes in this way brings us closer to the truth in understanding how animals perceive the world, and offers a unique opportunity to discover visual properties of habitats that no one ever thought to look for.
Urbanisation and Animal Behaviour
More and more people live in cities. Such urbanization has vast consequences on wildlife, both on community and individual level. In order to cope with changed environmental conditions in urbanised areas individuals need to be able to tolerate disturbances. One may expect that especially exploratory and risk-prone individuals can cope with such conditions. We assess ground beetles’ behavioural responses to urbanisation in city forests. Understanding individuals’ behavioural responses to environmental changes is essential for identifying which species may adapt to changing conditions or disappear from changed habitats, since behaviour is often the first response to altered conditions with subsequent consequences on fitness and population dynamics.
Group dynamics in subsocial cannibals
Spiders are notorious for their predatory lifestyle including cannibalism. Less than 5% of spider species evolved permanent sociality and they generally stem from subsocial ancestors in which offspring from a female stays together for a period of time. Most of such cases evolved in web-building spiders. Australian crabspiders from two genera (Australomisida and Xysticus) form an interesting exception as these spiders do not build webs but broods share a leaf nest for the entire developmental period. Such groups are generally related but unrelated intruders occur regularly and are tolerated in the nests. We are interested in the social organisation of these groups and we study hunting and feeding interactions in experimentally manipulated situations. We found cooperation and task partitioning during foraging and interesting dynamics of producer and scrounger specialisations.