Vicariance underlies allopatric speciation in Snapping Shrimp

1. Vicariance underlies allopatric speciation in Snapping Shrimp By Fred Singer

2. Allopatric speciation • 1. Physical barrier causes isolation of one population from a second population. • 2. Genetic divergence (usually in habitat use, resource use or mate choice). • 3. Reproductive isolation

3. Physical isolation • 1. Dispersal of a population to a new area. • 2. Vicariance – Changing of a habitat by geological processes into two distinct habitats.

6. Snapping Shrimp - Alpheus

7. Nancy Knowlton et al. • Sister species (sibling species) – two species that are very closely related • Sister species usually are initially identified by similarities in morphology (morphospecies). • In the case of snapping shrimp, characters included: • Dorsal spots • Dorsal bands • Antenna color • Movable spines

8. Knowlton’s hypothesis • Vicariance (formation of the isthmus 3-4 million years ago) caused physical isolation of populations of these species, leading to allopatric speciation. • This resulted in seven pairs of sister species

9. Prediction 1 • Sister species (based on morphology) should also be genetically more closely related to each other, than they are to other species • mtDNA (Cytochrome oxidase 1) • 11 polymorphic allozymes

10. mtDNA tree

11. Conclusion • Based on the mtDNA, sister species identified by morphological characters are also closely related based on mtDNA analysis

12. Prediction 2 • Because there was one vicariance event 3-4 million years ago, all seven sister species should have similar values separating the two sister species in relation to • mtDNA distance • allozyme distance • Similarities in mating behavior

13. Genetic Distances between sister species

14. Behavioral compatibility measures

15. Conclusion • The data do not support prediction 2 of the vicariance hypothesis. • Rather some sister species (e.g. P1 and C1, and P2 and C2) are more similar to each other genetically and behaviorally than other sister species (such as P7 and C7). • These differences are consistent for all three measures (allozymes, mtDNA, behavior) • Thus P1 and C1 speciated more recently than P7 and C7. • Thus there was a different timing of speciation for each sister pair.

16. Huh? • Doesn’t vicariance predict that each sister pair should show similar levels of genetic and behavioral divergence? • We need to consider ecology!! • In particular, different species prefer different hangouts.

17. http://www.vtmagazine.vt.edu/spring05/images/bubs.jpg

19. Conclusion • Vicariance has created the physical barrier for numerous speciation events in snapping shrimp. • We need to consider differences in ecology, in order to understand the sequence and timing of these speciation events.