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Welcome to the Krug lab at Cal State Los Angeles. We study the ecology and evolution of marine animals, focusing

 on the ecological and evolutionary role of dispersal by planktonic larval stages. We seek to understand how dispersal

 and habitat selection by larvae link populations, and to identify factors that limit gene flow, set range limits, and promote

 speciation in the sea. The lab uses a group of herbivorous sea slugs as a model system to understand the general forces

 that influence the evolution of marine life histories and impact coastal population dynamics.  Click on the major research

 topics (below) or the links on the left to learn more about our research.

 

 1. Range limits of estuarine animals

Some of our work examines the evolutionary ecology

 of range limits, to understand how physical stress  

 (heat, low salinity), biological interactions (competition),

 and coastal currents that deliver larvae together

 define the limits within which a species occurs.  This

 work will lead to better predictions of ecosystem

 response to ongoing climate change.  We use two

 species in the genus Alderia as a model system for 

 studies along the Californian coast.

A sampler of sacoglossan diversity

 

Alderia willowi

 

 

2. Phylogenetics and evolution of the Sacoglossa, solar-powered sea slugs  

 

 We use DNA sequences to infer the phylogeny, or "family tree", of a sea slug group called sacoglossans, an exciting group with which to study key evolutionary processes.  Most are herbivores that feed, mate and lay eggs on a species-specific host algae.  We are investigating how traits like larval type and algal host use have influenced speciation and lineage diversification, and how traits have changed over the history of this intriguing group.

   

Some sacoglossans exhibit kleptoplasty, the remarkable ability to store chloroplasts (the part of plant and algal cells

 that perform photosynthesis) from their meals. Instead of being digested, the hijacked chloroplasts continue to pump

out nutrients for the slug, in some species for many months. We are modeling how kleptoplasty evolves and affects

patterns of species richness in Sacoglossa.

 

3. Causes and consequences of shifts in larval development

 

Marine invertebrates have a two-stage life cycle, with non-reproductive

  larval stages that metamorphose into the adult form.  Feeding larvae

  (termed planktotrophic) develop in the plankton for long periods of

  time, during which they are dispersed by ocean currents.  Dispersal

  maintains gene flow and allows colonization of new habitats in species

  with limited adult mobility (think clams.. where's a clam gonna go?) 

 

Repeatedly in most animal groups, some species have evolved larvae that

 complete development without feeding (lecithotrophic larvae), and spend

  comparatively little time in the plankton; lecithotrophs do not disperse as far. 

 

Why some species lose dispersive larvae from their life cycle remains a puzzle. 

 Theory predicts dramatic effects of such transitions on population dynamics,

 gene flow, speciation, range size, and rates of molecular evolution.  We study

  the causes of evolutionary shifts in larval type in two ways: (1) using rare species

  that express both types of larval development at different times or places, and

 (2) by identifying traits associated with such shifts over evolutionary time.

 

 We also study the consequences of shifts to non-dispersing larvae for (1) the

 population genetic structure of related, ecologically similar species that differ

 in their larval lifespan, and (2) reproductive compatibility and genetic diversity

top: veliger larva of a snail                     among populations in species that produce alternative larval types.

bottom: egg mass of the sea               

  slug Elysia subornata, with a               

  colorful ribbon of orange yolk           

 

 All images Patrick Krug.