Thumb’s out when the mite Spadiseius calyptrogynae needs to move to a new host plant. It can’t get their on it’s own, so it simply hitchhikes on bees, bats or beetles. Emanuel H. Fronhofer and co-workes have studied this in the new Early View paper “Picky hitch-hikers: vector choice leads to directed dispersal and fat-tailed kernels in a passively dispersing mite“. Here is Emanuel’s summary of the exciting study:
Tropical species diversity can be so high that while walking through a lowland rainforest it may be difficult to see two individuals of the same tree species. This phenomenon has fascinated generations of naturalists, but at the same time such high diversity represents a considerable challenge for any organism that, because of its biology, has to find another tree of a certain species to feed on, for example. How do specialized mutualists, predators or parasites manage to find their host(s)? This problem is especially relevant and critical for a lot of small, non-mobile species that occupy ephemeral habitats, such as small ponds, dung or, as in this study, flowers.
In this context, we have studied the dispersal strategies of a neotropical phoretic flower mite, that uses a number of different animal vectors – bats, beetles and bees – in order to hitch-hike from one host plant to the next. These mites (Spadiseius calyptrogynae) are specialized to their host plant, an understorey palm (Calyptrogyne ghiesbreghtiana), while the flower visitors and potential dispersal vectors are generalists.
Using a dual approach that combines field observations with experiments and individual-based modelling we find that our study species shows a highly developed capacity to discriminate between potential dispersal vectors based on chemical cues. These mites choose their dispersal vectors in order to optimize their dispersal kernel, i.e. the distribution of dispersal distances. The evolutionarily stable dispersal kernel is a mixed kernel resulting from short distance dispersal with bees (Trigona fulviventris) and rare long distance dispersal events with beetles (Chasmodia collaris). This results in a fat-tailed distribution of dispersal distances and additionally guarantees directed dispersal towards especially suitable habitat, as the short distance dispersers prefer young over old flowers.
Besides being an example of information use for making dispersal decisions, we show how passive dispersers may realize directed and long distance dispersal. Furthermore, our study highlights the benefits of combining field work and individual-based modelling or theoretical approaches in general.