Freshwater crayfishes

Following the introduction to my thesis topic, I want to share one of my side projects focusing on freshwater crayfish. Freshwaters are highly threatened, yet some of the most poorly-known habitats on earth – enough to tickle my fancy! 

Freshwater invertebrates are a highly diverse group of animals, with more than 90,000 species described from 17 phyla and ~570 families. Invertebrates play crucial roles in the functioning of freshwater ecosystems, regulating decomposition, water clarity and nutrient cycling in lakes and streams. They are important prey for fish and other vertebrates that live in or around the water. Some invertebrates, such as mussels and decapod crustaceans are also harvested extensively by humans. Despite their diversity and ecological importance, freshwater invertebrates are largely under-studied, and even the better-studied groups receive less than a tenth of the attention given to freshwater fish. This lack of knowledge has severely hampered general scientific research on the evolution of these organisms, but also the conservation of freshwater ecosystems.

The analysis of large-scale patterns, as opposed to the study of local species and populations, is likely to be particularly suited to invertebrates as it offers more widely applicable results whilst taking into account differences among phylogenetic and geographical subsets. Macroecological and macroevolutionary studies could reveal drivers of diversification and extinction in invertebrates, which would not only contribute to scientific knowledge but also inform their conservation. Such studies of invertebrates are in their infancy: available data for invertebrates are similar to data available 15 or 20 years ago for birds and mammals.

Freshwater crayfish species richness. Scale: 0-11 species.
Freshwater crayfish species richness. Scale: 0-11 species.
Crayfish phylogeny, from Crandall (2008) Hydrobiologia
Crayfish phylogeny, from Crandall (2008) Hydrobiologia

Freshwater crayfish could provide a good starting point for global analyses in freshwater invertebrates. Freshwater crayfish are relatively species-poor (590 species) and are well-studied, due to the location of their two centres of diversity in developed countries (the USA and Australia). Their phylogeny is well defined and the focus of current research. IUCN range maps are also available for most crayfish species.

My project focuses on collating morphological and life-history information across crayfish species globally.

Combining these data with a phylogeny and range maps could answer a range of macroevolutionary and macroecological questions:

– What are the correlates of morphological evolution in crayfishes? I am especially interested in the evolution of chelae, due to their role in aggressive behaviour, competition and invasion.

– What are the correlates of diversification?

– What are the correlates of contemporary extinction risk?

– What are the correlates of invasion?

The task at hand, in Museum Victoria
The task at hand, in Museum Victoria

I am collecting information on eight life-history traits, such as maximum body size and maximum egg number. I am also collecting fifteen body measurements relating to carapace morphology and chelae morphology. I collate data from a range of sources, such as species descriptions, field guides and museum annals, and have accumulated a taxonomic library of around 300 references. I am also measuring freshwater crayfish from museums, and so far have visited the Natural History Museum in London, Museum d’Histoire Naturelle Paris and Museum Victoria. My database contains around 1800 specimens from 520 species, and hopefully I can collect some more!

Tracing the story of specimens
Tracing the story of specimens
Freshwater monsters, in Museum Victoria
Freshwater monsters, in Museum Victoria
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