Ossification and behaviour, do they interact?


With calcein vital stains and using UV light, it is possible to see the skeleton of young fish very well, while they don't need to be anesthesised or x-rayed.


calcein.jpg(Photo Craig Albertson)

We have two systems in the lab where such observations can be very useful to help us answer research questions on interactions between morphology and behaviour:

- Annual killifish sometimes show cannibalism as fry. Very often the cannibals grow to much larger sizes than their non-cannibalising kin. Is cannibalism inducing morphological allometric changes in the head, such that cannibals start looking more like related piscivorous species?


- Scale-eating cichlids often have asymmetric beaks, pointing either to the left or to the right. That is supposed to make them more efficient when attacking prey to rip some scales off their flanks. Is this asymmetry present from early ossification? Or is it determined by behavioural preferences, such that young scale-eaters are still rather symmetric?


This is a project for a Bsc. or Msc. student. In collaboration with the technical workshop, the student will build a setup where behaviour of fry can be observed and photographs of the skeleton made. This setup will be tested and improved using fry of annual killifish, of which we have a steady weekly supply. Then an experiment using fry of scale-eating cichlids will be carried out.

Supervision is by Tom JM Van Dooren (t.j.m.van.dooren@biology.leidenuniv.nl)


Handedness in scale-eating cichlids: is it in the bones?


Scale-eating cichlids from Lake Tanganyika offer an inspiring example of frequency-dependent selection in action. Adults of P. microlepis are either left-handed, with a beak oriented towards the left, or right-handed, with their beak towards the right.

Lef-handed fish attack the right flanks of prey, right-handed fish the left flanks. Frequency dependence is caused by the prey: when one scale-eating morph is rare, the prey doesn't expect attacks from the corresponding side, giving a rarity advantage.



It is believed that handedness is caused by one major gene with dominance-recessivity. In our lab, however, we discovered that that cannot be true. We also find many rather symmetric fish, such that handedness in scale-eating cichlids might just be another example of fluctuating asymmetry.

Our measures of handedness so far are based on morphometric analysis of head outlines (contours). Old papers on P. eccentricus claim that there was a clear handedness in the jaw bones.


We now want to complement our contour morphometrics with an analysis of jaw bone variation, to check whether they are concordant or not, whether jaw bone asymmetry is more discrete than our contour measures, and whether jaw bone asymmetry correlates with differences in attack behaviour.


This is a six-month project for a Msc student. The student will do attack preference experiments, morphometrics from digital photographs of heads, and from x-ray photographs.

Supervision is by Tom JM Van Dooren (t.j.m.van.dooren@biology.leidenuniv.nl) and Frans Witte.


Braconid parasitoids of Drosophila lay their eggs in the larvae of Drosophila. They are represented on all continents. As Drosophila melanogaster has now a cosmopolitan distribution this species has become an important host for many Asobara species. Currently we keep 5 species in our laboratory: Asobara tabida, a palearctic species, A. citri, an African species, A. japonicus from Japan, A. pleuralis from Indonesia and A. persimilis from Australia.  Although D. melanogaster has the same developmental period from egg to adult in worldwide, the 5 Asobara species differ markedly in developmental time, from 21 days in A.tabida to 12 days in A. pleuralis, measured at 25 C, with the other species having intermediate developmental times. This poses the question which selective pressures act on developmental time, and which constraints prevent species to have shorter developemental times. Our hypothesis is that a shorter developmental time has costs, because it is traded off against other life-history characters, like fecundity or longevity.
The practical work involves measuring of size, weight, egg load, fecundity and lipoprotein contents of Asobara wasps reared under standard laboratory conditions.

This project can be done as BSc stage (4 months), or be extended to a MSc research project.


Supervision: Majeed Askari Seyahooei & Jacques van Alphen

Contact: m.a.seyahooei@biology.leidenuniv.nl      


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