Model Organisms

Astyanax mexicanus

Astyanax mexicanus is a teleost fish that lives in rivers of central and North America (surface fish, SF) and in about 30 caves in northeastern Mexico ( cavefish, PA). Cave populations have evolved from surface fish and have developed numerous adaptations to subterranean lifestyle, including loss of eyes and pigmentation, elaboration of non-visual sensory systems, altered metabolism, neurological adaptations, altered behaviors, etc.

Several cave populations have evolved independently from their surface ancestors, allowing the study of convergence and parallel evolution. Despite many differences, cavefish and surface fish are still able to interbreed and produce fertile offspring (HY), allowing genetic studies of cave-adapted traits.

The Mexican cave tetra can be reared on a simple diet, produces large numbers of embryos, and has a relatively short generation time, making it a suitable laboratory organism. Therefore, the Mexican cave tetra has recently become an important evolutionary and developmental model organism.

Resources available for its studies include sequenced genomes of both the cave and surface forms, developmental staging table, methods for breeding, transgenesis, and gene editing.

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Telestes karsticus

Telestes karsticus, photo: Branko Jalžić

There are a total of 14 species of the fish genus Telestes in the family Cyprinidae, three of which are endemic to Croatia: T. fontinalis, T. karsticus and T. polylepis.

We are interested in the karstic dace (T. karsticus) because it forms cave populations in addition to surface populations. The species occurs only in four localities in the karst areas of the Velika and Mala Kapela mountains.

Even at first glance, the cave and surface forms show clear differences in size and degree of pigmentation, making this species a suitable model for understanding the initial stages of cave colonization.

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Genus Proasellus

Proasellus hercegovinensis, photo Lada Jovović

Proasellus is a globally distributed genus of freshwater isopods in the family Asellidae. The total number of subterranean species worldwide is 115.

The biology of these subterranean populations is not well known, but they probably live in interstitial habitats and feed on dead organic material, as well as bacteria and fungi that grow on it. In general, groundwater species exhibit a number of adaptations: morphological (depigmentation and anophthalmia), physiological (low metabolic rate), and life history (delayed sexual maturity and reduced fecundity).

We are culturing two subterranean species, P. anophthalmus and P. hercegovinensis, as well as two related surface species, P. karamani and P. coxalis, in our laboratory.

Our experiments showed that ommochromes are the main body pigments in the aboveground species. Our goal is to determine the precise mechanisms leading to albinism as a result of ommochrome deficiency in cave dwellers.

To achieve this, we combine biochemical methods in collaboration with Florent Figon (University of Tours, France) and genomic approaches in collaboration with Florian Malard and Tristan Lefebure (University of Lion, France).

In addition, we are interested in cave colonization and use surface species as proxies for the ancestors of cave lineages in long-term evolutionary experiments.

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Asellus aquaticus

The aquatic isopod Asellus aquaticus, is distributed over most of Europe. It inhabits almost all freshwater habitats, as well as slightly brackish and polluted waters. 

Asellus invades caves throughout its range and has independently established several stable cave populations. However, highly troglomorphic Asellus sp. have been found in only three regions: Slovenia, Hungary and Romania.

A dozen other populations exhibit varying degrees of cave adaptations. The most obvious are morphological changes such as the loss of pigment and eyes, body enlargement, but there are many changes in behaviors and physiology as well such as feeding and sheltering related behaviors, metabolic rates, enzymes activities.

In addition, some of the cave and surface populations can be interbred allowing for a genetic analysis of adaptive traits in cave Asellus. All of this makes Asellus an ideal model system for subterranean evolutionary experiments.

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Trichoniscids

Trichoniscus matulici (left) and T. pusillus (right), photo Jana Bedek

Terrestrial isopods of the family Trichoniscidae are among the most abundant animals in caves. The cave species Titanethes albus and Alpioniscus spp. are widely distributed along the Dinaric Karst.

Titanethes albus is endemic to the Dinarides. In contrast, the genus Alpioniscus, with 40 species, is disjunctively distributed across southern Europe from Greece to Spain. Both genera are highly troglomorphic, lacking pigment and eyes, and have only distant surface relatives. Therefore, we use the aboveground Trichoniscus and Hyloniscus, for comparison in our experiments.

Trichoniscus matulici is a transadriatic species distributed in the Balkans, Malta and Italy including Sicily. As a highly higrophilous species, it invades caves throughout the area and is capable of forming stable cave populations.

Cave populations show more or less pronounced troglomorphic features such as body depigmentation and eye deterioration. Consequently, Trichoniscus is a suitable model system for understanding the process of cave colonization and adaptation.

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Sphaeromatids

Monolistra radjai and Lekanesphaera sp., photo Jana Bedek

The cave isopods Monolistra (family Sphaeromatidae) are exclusively distributed in the Dinarides. There is a total of 21 obligate cave species, and all are depigmented and blind.

They inhabit cave freshwaters, with the exception of M. radjai, which can tolerate brackish water and is also found in anchialine caves. Like most isopods, they probably feed on dead organic matter, from shredding leaf litter to scavenging on various invertebrates.

The closest surface relatives are marine sphaeromatids, but currently the data on their exact relationships is still missing. In our lab we use Adriatic Sphaeroma sp. and Lekanesphaera sp. as surface relatives of Monolistra.

Many aspects of the biology of Monolistra are unknown, but their highly evolved adaptations, and widespread occurrence makes them a good model system for studying aspects of cave biology such as the loss of pigmentation.