How do new species arise and maintain their integrity?

Species generally arise when gene flow is disrupted by a geological or oceanographic barrier. When species come in contact again, they will not merge if they have evolved differences that prevent the transfer of genes. Examples in marine organisms might be specialization in different habitats, difference in spawning cycles, incompatibility of gametes, or developmental dysfunction of hybrids.

What molecules confer compatibility of gametes of the same species and incompatibility between gametes of different species?

We focus on sea urchins (model organisms for developmental biology), because their external fertilization greatly simplifies the number of factors that need to be taken into account. My colleagues and I are studying the evolution of bindin, a molecule on the sperm that is recognized by the egg, and EBR1 and the “350kD protein”, two molecules on the egg that interact with bindin to effect fertilization. To a lesser extent, we have also worked with speract, a molecule released by the egg to attract sperm, as well as its receptor on the sperm.

What are the evolutionary forces that result in barriers to genetic exchange between species?

Species are sets of populations reproductively isolated from other populations, so speciation is the evolution of barriers to genetic exchange. Such barriers need not be molecular interactions of gametes. A long-term study of two genera of sea urchins each with two sympatric sister species in the Caribbean is seeking to establish whether these species occupy different habitats, whether they reproduce at different times (and the factors that control their reproduction), whether their gametes are incompatible, or whether their hybrids are developmentally unstable (and the genes responsible for their lower fitness).

B.A., Harvard College, 1973

M.Phil., Yale University, 1976

Ph.D., Yale University, 1979

H. A. Lessios. 2016a. The great Diadema antillarum die-off: 30 years later. Annual Review of Marine Science 8:267-283 doi:10.1146/annurev-marine-122414-033857

H. A. Lessios and I. Baums. 2016. Gene flow in coral reef organisms of the tropical eastern Pacific. In: P.W. Glynn, I.C. Enochs, and D. Manzello (eds.) pp. 477-499 In: Coral Reefs of the Eastern Pacific. Springer-Verlag. DOI: 10.1007/978-94-017-7499-4_16

H.A. Lessios. 2011. Speciation genes in free-spawning marine invertebrates. Integrative and Comparative Biology, 51:456-465.

H.A. Lessios. 2008. The Great American Schism: Divergence of marine organisms after the rise of the Central American Isthmus. Annual Review of Ecology, Evolution, and Systematics, 39(1): 63-91.

H.A. Lessios and D.R. Robertson. 2006. Crossing the impassable: genetic connections in 20 reef fishes across the Eastern Pacific Barrier. Proceedings of the Royal Society, London series. B, 273: 2201-2208.

H.A. Lessios, B.D. Kessing, J.S. Pierce. 2001. Population structure and speciation in tropical seas: global phylogeography of the sea urchin Diadema. Evolution, 55:955-975.

H.A. Lessios, D.R. Robertson, J.D. Cubit. 1984. Spread of Diadema mass mortality through the Caribbean. Science, 226:335-337.

Back to Top