Dispersal and diversification in freshwater environments

Animals that inhabit freshwaters must deal with the unique challenges of living in such environments.

Our research examines how freshwater inhabitants disperse and diversify - two fundamental issues for understanding biodiversity.

Dealing with change

Freshwater habitats change over time and are often isolated – yet they are widely inhabited. Our research focuses on how organisms find new suitable sites and how dispersal links populations across the landscape. 

We are especially interested in the mechanisms and consequences of dispersal for invertebrates with poor locomotory powers (freshwater bryozoans and their parasites) and use fieldwork and molecular tools to address the following questions:

• Are resistant resting stages of bryozoans (statoblasts) dispersed by waterfowl?
• How does variation in dispersal capacity relate to diversification?
• Does dispersal frequency vary in bryozoans that inhabit lakes vs. rivers?
• What strategies do parasites use to disperse with their bryozoan hosts?
• Can bryozoans escape parasites by dispersing to new sites?

Freshwater bryozoan biodiversity

Bryozoans form colonies composed of tiny (~1mm) iterated modules called zooids whose tentacular crowns create feeding currents to capture microscopic organisms.  

Phylactolaemate bryozoans are restricted to and ubiquitous in freshwaters. Their feeding activities link planktonic productivity to benthic habitats and attract tiny invertebrates and micro-organisms that also utilise them. A few ctenostome bryozoans have invaded freshwater habitats from the sea.

Freshwater bryozoan biodiversity is poorly known. Recent expeditions to Thailand, Borneo, South Africa and Brazil have enabled the discovery of novel diversity and greatly expanded the Natural History Museum’s collections. Ongoing research on bryozoan diversification includes:

• diversity of freshwater bryozoans in the Amazon basin
• taxonomy and systematics of phylactolaemate bryozoans
• ctenostome phylogeny and evolution.

Parasite evolution and diversification

We are examining how myxozoans have evolved to parasitise bryozoan hosts and the origins and radiations of myxozoans in freshwater environments.

Bryozoans offer parasites a potentially unlimited, genetically homogenous resource. Our research exploring how myxozoans exploit this resource includes:

• cycling between developmental stages depending on host condition
• local adaptation between parasites and hosts.

Myxozoans have adopted freshwater hosts on multiple occasions. We are examining the associated radiations in freshwater environments, including: 

• morphological simplification of myxozoans that exploit bryozoan hosts (from active worms to inert sacs)
• the evolution of vermiform plasmodia in South America
• origins of myxozoan radiations in freshwater environments.