Presentation Detail

Speciation

Lackey, Alycia [1], Boughman, Jenny [1].

Comparing contributions to reproductive isolation for intact and collapsed stickleback species pairs.

The speciation process has been studied for decades, but we still know little about the relative importance of different reproductive barriers. This is essential for understanding which barriers contribute most to the evolution and maintenance of distinct species. We also lack a detailed understanding of how the environment, and environmental change, impacts speciation. If important reproductive barriers depend on environmental differences, then environmental change may break down isolation between species and cause species loss. We measured the strength of eleven reproductive barriers, including prezygotic, postzygotic, extrinsic (environmentally-dependent) and intrinsic barriers, in multiple species pairs of threespine stickleback fish. Limnetic-benthic stickleback species pairs evolved in parallel in seven freshwater lakes in British Columbia, Canada, and so serve as replicate populations. One of these species pairs has recently collapsed into a hybrid swarm after the introduction of an invasive crayfish 30 years ago. Stickleback species pairs diverged recently within the past 15,000 years. Current barriers between these young species were likely important for speciation to occur, and any barriers lost after hybridization began were likely important to maintain species. Thus, this stickleback species pair system provides a rare opportunity to study speciation both as it proceeds and breaks down. For currently isolated species pairs, reproductive isolation is strong and nearly complete. Both prezygotic and postzygotic extrinsic barriers are strong, especially spatial isolation, sexual isolation, and selection against hybrids. In contrast, intrinsic barriers of gametic and genetic incompatibilities have no effect on overall isolation. Multiple barriers with intermediate strength suggest that reproductive isolation evolves gradually in this system. In the formerly isolated species pairs, most reproductive barriers are nonexistent, though spatial and weak sexual isolation remain. This demonstrates that individual barriers as well as overall isolation can quickly erode in just 30 generations. The fast and substantial loss of reproductive isolation in one species pair after an environmental disturbance suggests that intrinsic barriers may be necessary to maintain species when environmental differences that likely promoted species divergence are lost.

1 - Michigan State University, Zoology, 203 Natural Science Building, East Lansing, MI, 48824, USA

Keywords:
reproductive isolation
Speciation
prezygotic
postzygotic
stickleback
intrinsic
extrinsic
environmental change.

Presentation Type: Regular Oral Presentation
Session: 110
Location: Cotton C/Snowbird Center
Date: Monday, June 24th, 2013
Time: 10:30 AM
Number: 110001
Abstract ID:140
Candidate for Awards:W.D. Hamilton Award for Outstanding Student Presentation,Student Travel Awards from the ASN