Dickel, L. | bioRxiv Science

bioRxiv2020

Characterization of habitat requirements of European fishing spiders

Wetlands are among the most threatened habitats in the world, and so are their species, which suffer habitat loss due to climate and land use changes. Freshwater species and arthropods receive little attention in research and conservation, and the goals to stop and reverse the destruction of wetlands published 25 years ago in a manifesto by the Union of Concerned Scientists have not been reached. In this study, we investigated the occurrence and habitat requirements at two spatial scales of two species of European fishing spiders Dolomedes, which rely heavily on declining wetland habitats in Sweden and southern Norway. We collected occurrence data for Dolomedes plantarius and Dolomedes fimbriatus, using a live-determination-method. We modelled the placement of nursery webs to describe fine scaled habitat requirements related to vegetation and microclimate. Using a machine learning approach, we described the habitat features for each species, and for co-occurrence sites, to provide insight into variables relevant for the detectability of Dolomedes. We found that habitat requirements were narrower for D. plantarius compared to D. fimbriatus; that the detection of nursery webs can be affected by weather conditions and that nursery placement is mostly dependent on the proximity to water, the presence of Carex sp. (Sedges) and of crossing vegetation structures, and on humidity. Furthermore, co-occurring sites were more similar to D. plantarius sites than to D. fimbriatus sites, whereby surrounding forest, water type and velocity, elevation and latitude were of importance for explaining which species of Dolomedes was present. We provide a detailed field protocol for Dolomedes studies, including a novel live-determination method, and recommendations for future field protocols.

ecology↗

bioRxiv2018

Awareness of danger inside the egg? Evidence of innate and learned predator recognition in cuttlefish embryo.

Predation exerts one of the greatest selective pressures on prey organisms. Many studies showed the existence of innate anti-predator responses mostly in early stages of juveniles vertebrate. Learning is also possible but risky since it can cause death. There is now growing evidence that embryonic learning exists in animals but few studies have tested explicitly for learning in embryos. Here, Sepia pharaonis cuttlefish embryos respond to the presence or odour of a predator fish but not to a non-predator fish. Interestingly, embryos can learn to associate a non-threatening stimulus with an alarm signal: cuttlefish ink. After several paired exposures, they respond to the harmless fish as if it were dangerous. Our results demonstrate both innate and acquired predator recognition in a cephalopod. Embryos response is a decrease of ventilation rate. Such response is adaptive, especially in a translucent egg, since it reduces movement and hence the risk of being detected; this freezing-like behaviour may also reduce bioelectric field, which lessens shark predation risk. Last, our result is the first report of associative learning in an invertebrate embryo. This shows that a cuttlefish embryo can have both genetic predator avoidance skills and possesses enough cognitive abilities plasticity to learn and retain new threats before hatching. The combination of these mechanisms is an impressive example of the early adaptability of cephalopod molluscs. This amount of behavioural plasticity gives the newly-hatched sepia a huge selective advantage when dealing with known or new threats.

animal behavior and cognition↗