Herp Meetings 2013 Day 1: Reproductive Isolation In Parapatric Subspecies Pairs

Slide from Anthony Geneva’s talk, showing the placement of the A. d. ravitergum and A. d. ignigularis crosses on the scale of reproductive isolation.

The Joint Meeting of Ichthyologists and Herpetologists kicked off this week in Albuquerque, NM. Anoles are well represented, with 7 posters and 5 talks. During the conference, I will report on some of the exciting work being presented.

Anthony Geneva, Ph.D. student in Rich Glor’s lab at the University of Rochester, gave a proper introduction to the meetings with his talk Friday morning. Anthony’s study investigates the degree of reproductive isolation in the parapatric subspecies pair A. disticus ravitergum and A. d. ignigularis. Each subspecies is genetically and morphologically distinct, though not completely isolated. Along the pair’s contact zone, there is a clinal gradient from a pure red (ignigularis) to a pure white (ravitergum) dewlap. Evidence for introgression in mtDNA haplotypes also follows this clinal pattern, with hybrids existing in the middle of the range. This provides an excellent model system for studying the process of speciation.

Anthony used a classic genetic cross to search for evidence for intrinsic isolating mechanisms in the subspecies pair. The product of these crosses was a whopping 1702 eggs and 857 babies. One convincing result was that hybrid crosses produced a greater proportion of slug (unfertilized eggs) than pure crosses! These results suggest that the barrier preventing coalescence is post-mating, prezygotic isolation. He was able to quantify the degree of intrinsic isolation on the index above, with 0 representing no isolation and 1 representing complete isolation. On this index, the focal Anolis disticus subspecies pair is placed in between the classic speciation model systems of Ficedula flycatchers and Rhagoletis apple maggots.

The presence of post-mating pre-zygotic isolating mechanisms suggests that cryptic female choice and sexual selection play a role in separating the two subspecies. Anthony plans to continue this work by backcrossing hybrid individuals to pure individuals, and hopes to use genetic cline analysis to identify the genomic regions underlying intrinsic isolation.

Over the next few days, I will also post about some of the other Anolis talks and posters here at the JMIH. Check back soon!