Copulating pair of Lumbricus terrestris, the common earthworm or dewworm. It is widespread, easy to keep, ecologically well-studied, but poorly known when it comes to reproductive strategies. Earthworms are very important for agriculture and soil ecology in general. What many people do not know, however, is that they are heavily parasitised, very sensitive to stress, and very choosy when it comes to partners, food or a place to live.

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Caenorhabditis elegans is a free-living soil nematode, which feeds on micro-organisms primarily in decaying material (e.g. compost heaps). It has become one of the main model organisms in biological research due to its advantages as an experimental system: It can be easily maintained and manipulated in the laboratory. It is transparent, such that phenotypes can be scored using simple microscopy. It has a short generation time, thus facilitating performance of crossing experiments. And a whole array of molecular genetic methods and the complete genome sequence is available. In our department, it is used as a model host to study the evolutionary dynamics of parasite-host interactions. The photograph shows a fluorescent micrograph of C. elegans in which nuclei are stained with the DAPI reagent (photograph by Sebastian Hering).

Caenorhabditis remanei is a 1 mm long, terrestrial nematode found on rotting fruits where it feeds on bacteria and fungi. In contrast to C. elegans, C. remanei is a gonochoric (male-and-female) species, with obligate, frequent mating. Females lay around 500 eggs per lifetime. The development from egg to adult takes three days at 22 °C. Adults live for about 2 weeks. They show a variety of traits related to reproduction, such as pheromones or mating plugs. The picture shows a mating pair (female on the left, male on the right).

Opisthobranch sea slugs (families Aglajidae and Gastropteridae) display an intriguing diversity of mating mechanisms. These range from seemingly peaceful reciprocation to apparently enforced unilateral matings, and may involve rather aggressive biting, hypdermic injections, and elaborate penial armature. This group therefore provides an excellent system to investigate the evolutionary dynamics of hermaphrodite mating mechanisms among closely related species. Moreover, their anatomy allows convenient manipulation of mating interests, e.g. by interrupting sperm transfer, enabling elegant experimental studies on topics such as sperm trading.

There are many species of reef fish in several genera that fluoresce in red. This phenomenon occurs most frequently in the families of the Gobiidae, Tripterygiidae, Syngnathidae and Labridae. In our laboratory, we mainly work on two species: the pygmy goby Eviota pellucida and the pipefish Corythoichthys intestinalis.

E. pellucida is a small benthic fish reachig about 3,5 cm in total lenght. It tends to live in small groups on rubble associated with coral reefs in the Indo-pacific.

C. intestinalis is also a benthic species which, in contrast to pipefish of other genera, spends most of the time lying on sand. These pipefish are food specialists, hunting for the smallest organisms living on the ground all day long. Sex roles in pipefishes are reversed, meaning that the males are the ones to carry out eggs in a brood pouch to "give birth" to fully developed young pipefish. This sex role reversal also led to a very interesting courtship behaviour.

Small robots in large numbers are used as a population of artificial organisms to investigate reproductive strategies. Such robots operate autonomously by carring their own processor and battery and are programmed to behave like a model organism for complex experiments.

The robots shown on the picture, called the Jasmine III, are little, cubic robots with a length of about 2.5 cm. These robots are driven by 2 wheels and have 6 infrared emitters and sensors to detect obstacles and communicate with other robots. About 30 of these robots are used in experiments where they evolve their behaviour. During their life time they have to mate and produce offspring before they die. When a robot is dead, it can be revived as the offspring of another robot. In this system, hermaphroditic and gonochoristic behaviour has been created to compare these two different reproductive strategies.