Biomedical subjects

Joachim G Frommen

Publications and source records attributed to Joachim G Frommen.

3 recordsLinked to original sources

PubMed2006

Infection with an acanthocephalan manipulates an amphipod's reaction to a fish predator's odours.

Many parasites with complex life cycles increase the chances of reaching a final host by adapting strategies to manipulate their intermediate host's appearance, condition or behaviour. The acanthocephalan parasite Pomphorhynchus laevis uses freshwater amphipods as intermediate hosts before reaching sexual maturity in predatory fish. We performed a series of choice experiments with infected and uninfected Gammarus pulex in order to distinguish between the effects of visual and olfactory predator cues on parasite-induced changes in host behaviour. When both visual and olfactory cues, as well as only olfactory cues were offered, infected and uninfected G. pulex showed significantly different preferences for the predator or the non-predator side. Uninfected individuals significantly avoided predator odours while infected individuals significantly preferred the side with predator odours. When only visual contact with a predator was allowed, infected and uninfected gammarids behaved similarly and had no significant preference. Thus, we believe we show for the first time that P. laevis increases its chance to reach a final host by olfactory-triggered manipulation of the anti-predator behaviour of its intermediate host.

Acanthocephala↗

PubMed2006

Inbreeding avoidance through non-random mating in sticklebacks.

Negative effects of inbreeding are well documented in a wide range of animal taxa. Hatching success and survival of inbred offspring is reduced in many species and inbred progeny are often less attractive to potential mates. Thus, individuals should avoid mating with close kin. However, experimental evidence for inbreeding avoidance through non-random mating in vertebrates is scarce. Here, we show that gravid female three-spined sticklebacks (Gasterosteus aculeatus) when given the choice between a courting familiar brother and a courting unfamiliar non-sib prefer to mate with the non-sib and thus avoid the disadvantages of incest. We controlled for differences in males' body size and red intensity of nuptial coloration. Thus, females adjust their courting behaviour to the risk of inbreeding.

Animals↗

PubMed2006

Slow fertilization of stickleback eggs: the result of sexual conflict?

BACKGROUND: The fertilization success in sperm competition in externally fertilizing fish depends on number and quality of sperm. The time delay between sequential ejaculations may further influence the outcome of sperm competition. Such a time interval can load the raffle over fertilization if fertilization takes place very fast. Short fertilization times are generally assumed for externally fertilizing fish such as the three-spined stickleback (Gasterosteus aculeatus). In this pair-spawning fish, territorial males often try to steal fertilizations in nests of neighbouring males. This sneaking behaviour causes sperm competition. Sneakers will only get a share of paternity when eggs are not fertilized immediately after sperm release. Contrary to males, females may be interested in multiple paternity of their clutch of eggs. There thus may be a sexual conflict over the speed of fertilization. RESULTS: In this study we used two different in vitro fertilization experiments to assess how fast eggs are fertilized in sticklebacks. We show that complete fertilization takes more than 5 min which is atypically long for externally fertilizing fishes. CONCLUSION: This result suggests that the time difference does not imply high costs to the second stickleback male to ejaculate. Slow fertilization (and concomitant prolonged longevity of sperm) may be the result of sexual conflict in which females aimed at complete fertilization and/or multiple paternity.

Animals↗