Evolutionary morphology in trichomycterid catfishes: structural and functional adaptations in haematophagous vertebrates
- Study object: Neotropical catfishes (Trichomycteridae), especially representatives of the clade showing an evolutionary trend towards haematophagy (including the legendary candirù catfish).
- Principal aim: understand the level of adaptive evolution in the cranial musculoskeletal system during evolution in relation to haematophagy.
- Methodology: clearing and staining, dissections, histology, micro-CT-scanning, graphical 3D-reconstructing, 3D-modelling of functionality, molecular phylogeny.
- Researcher: Dominique Adriaens
Scientific problem
Some of the most interesting feeding specialisations within the catfishes are found in the Neotropical
Trichomycteridae. Most of the representatives in this family are generalised predators. However, this family is often referred to
as the parasitic catfishes, referring to the lifestyle of the species found in two subfamilies, the Vandellinae and Stegophilinae
(see Fig. 1).
Fig. 1: Cladogram of Trichomycteridae (based on de Pinna (1998)).
These two subfamilies contain species generally known as "candirù" (see Fig. 2), infamous in the Amazon basin.
These candirù are known to sporadically penetrate the human urethra.
Fig. 2: Head of a Vandellia cirrhosa (ANSP 178176).
Although the term parasitic or semi-parasitic applies to the clade Tridentinae-Stegophilinae-Vandellinae (clade G in
Fig. 1), both have a complete different way of feeding. Vandellinae appear to be exclusively haematophagous;
Stegophilinae, on the other hand, feed on mucus and scales of fish or scrap pieces of muscle tissue of their victims. Despite this
unique behaviour little is known of the head morphology and so far most studies have focussed on the osteology. Besides a recent
study on the cranial myology in Vandellia (in our research group) little is known on the myology. Furthermore, the phylogeny of
these Trichomycteridae is far from reliable and robust. Most research, however, are in urgent need of such reliable phylogenetic
hypotheses. Only then an interpretation can be made on the adaptations and neoformations of the many structures associated with the
specialised feeding apparatus.
Aims
Numerous studies already showed that the Siluriformes have developed into a successful group and this to some extend due to their large variation in trophic specialisations. As already mentioned, the parasitic feeding manner, typically for the Vandellinae and Stegophilinae is only limitedly studied. Within this study the feeding apparatus and opercular anchoring mechanism will be morphologically studied in detail and this in a robust phylogenetic framework. Such a multidisciplinary study is necessary to discuss the macro-evolution of these complex systems within the Trichomycteridae. The research strategy within this project can be split down in:
- to establish a phylogenetic framework, based on molecular data;
- a study on the morphology of the cranial musculo-skeletal system, focussing on the feeding apparatus and anchoring system (see see Fig. 3);
- use 3D-models and apply 3D-modelling (see Fig. 4) to understand mechanisms for anchoring and feeding, to evaluate to what degree the candirù morphology is the result of adaptive evolution towards a highly specialized way of feeding;
- a morphological and histochemical study of the digestive and urinary system.
Fig. 3: Overview of histological section through the head of Vandellia, showing a detail of the skin (inset).
Fig. 4: 3D-model of opercular system in Vandellia, showing hypothetical mechanism of opercular spine locking (click to see the movie).
