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Pernet Lab - Research |
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Evolution of maternal provisioning, cleavage patterns, and larval function in spiralians
Egg size is correlated with larval form and function in the many groups of marine invertebrates whose life cycles include larval stages - "small" eggs tend to develop into feeding larvae with complicated food gathering and digesting structures, and "large" eggs into nonfeeding larvae that often lack these structures. I am interested in understanding the developmental and evolutionary underpinnings of this correlation in animals that whose  embryos undergo spiral cleavage. Observations of the larval development of the sabellid annelid Schizobranchia insignis (a featherduster worm) led me to develop a hypothesis that links egg size to embryonic cleavage pattern, and cleavage pattern to the timing of development of the gut - and thus feeding ability - in spiralian larvae (for an early version of this idea, see Pernet [2003]). One of my current research projects is an attempt to test these ideas, mainly using explicitly comparative studies of associations between egg size, allocation to endodermal cell lineages, and the timing of gut development in annelids (like the Protula sp. larva shown on the left) and molluscs. I also hope to develop tests of these ideas using techniques of experimental embryology. Functional morphology of feeding by the larvae of marine annelids Many phyla of marine invertebrates contain species that have feeding larval stages in their life cycles. In most of these phyla, larval feeding mechanisms are fairly uniform among species. For example, all feeding echinoderm larvae that have been studied capture food particles in the same basic way, as do almost all feeding mollusc larvae. The phylum Annelida, however, is different. Feeding annelid larvae use a diversity of mostly undescribed mechanisms to capture food particles. Annelids present an excellent opportunity to test hypotheses on the functional consequences and evolution of larval feeding using comparative studies. I'm currently interested in addressing the following specific questions: 1. how widely distributed is "opposed band" or "downstream" larval feeding in the annelids? Can detailed morphological, developmental, and behavioral data, in the context of phylogenetic hypotheses, help us determine how frequently this feeding mechanism has evolved in this phylum? 2. how do the feeding larvae of phyllodocidan annelids capture particles? Phyllodocidans are a large clade of annelids whose larvae (so far as we know) do not capture particles with opposed bands. Instead, they seem to use diverse mechanisms that allow them to capture relatively large particles. Feeding has so far been described only in members of two (of approximately 20, not all of which include species with feeding larvae) families of phyllodocidans, the Polynoidae (Phillips and Pernet 1996) and the Chrysopetalidae (Pernet, unpublished). 3. what are the functional consequences (e.g., on rates of particle capture, or the kinds of particles that can be captured, and ultimately on larval developmental rates) of different larval feeding mechanisms? I address these questions using a combination of studies on larval morphology (with scanning electron microscopy as an important tool), particle paths around tethered or free-swimming larvae (video microscopy), and larval performance (feeding and growth experiments).
Biology of the exploited (and imported) ghost shrimp Neotrypaea californiensis in southern California The ghost shrimp N. californiensis is a common member of soft-sediment intertidal communities on the west coast of the United States, where it plays an important role as a major bioturbator, and as a food source for birds and fishes. Many southern California populations are frequently harvested by recreational fishers looking for bait, and to meet demand, N. californiensis are also imported into the region from Oregon and Washington. Since 2005, my lab group has studied risks associated with the importation of northern shrimp into southern California (e.g., homogenizing existing genetic structure in the species, or importing non-native parasites). These ongoing studies (funded by California Sea Grant) have also led us to address questions about the systematics, reproductive, and larval biology of ghost shrimp. Some of these studies are carried out with collaborators at the Cabrillo Marine Aquarium in San Pedro. Other projects on the natural history of marine invertebrates I spend a fair amount of time looking at invertebrate animals in the field and lab, often as a part of teaching. This frequently yields observations (by students, and by me) of novel and intriguing forms, behaviors, or distributions. These in turn often lead to questions that can be answered in field and lab studies. I try to spend some of my research effort answering such questions, in part because it's fun, and in part because answers often open up new areas of interest. I am also usually very happy to advise students in research projects that develop from such observations.
Last modified 30-Aug-07 |
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