Sulawesi's divergent tarsiers: The who, Why and How of gene flow in a secondary contact zone
Final Report Abstract
This project was designed to explore general evolutionary mechanisms in hybrid zones by evaluating patterns of dispersal, mate choice, hybridisation and introgression at a secondary contact zone of two cryptic Central Sulawesian tarsier species: How do closely related taxa withstand genetic homogenisation despite gene flow? With a comprehensive multidisciplinary approach, we uncovered crucial pieces of the mechanisms leading to largely assortative mating on one hand but also to some degree of hybridisation on the other hand. We found prezygotic isolation in terms of character displacement concerning tarsier songs as well as reinforced selectivity in reception of vocal signals. A significant discovery was that tarsier songs are inherited and not learned. As at least female hybrids perform songs that are (in several measurable parameters) intermediate between both species, it seems likely that through this pattern, mate recognition is facilitated and disadvantageous matings between “pure” individuals and hybrids are largely avoided. To our disappointment, labour‐intensive radio‐tracking in the hybrid zone did not allow general inferences of dispersal behaviour of young adults in relation to the species boundary’s course. However, ranging data, specifically the finding of no interspecific overlap of home ranges indicate that both species recognise each other as “similar” (ecological competitors) but not as suitable mates (see playback experiments). Microsatellite analyses confirm that matings between species are indeed rare (no F1 hybrids found). Our results so far support prior findings of asymmetric introgression as they revealed accordant asymmetry in reproductive barriers. Ongoing analyses of sequence markers will shed further light on this issue. The slight shifting of the hybrid zone within eight years (2005‐2013) might be a stochastic process as often seen in hybrid tension zones. The direction of this shift, however, interpreted in light of intensified habitat encroachment and findings of high adaptability of Dian’s tarsiers to human land‐use suggests that slow but constant competitive exclusion of T. lariang by T. dentatus goes along with habitat change. Another look at this boundary in a couple of years will be rewarding.
Publications
- (2012). Novel tetra‐ and pentanucleotide microsatellite markers allow for multiplexed genotyping of Sulawesi tarsiers (Tarsius spp.). Conservation Genetics Resources 4:343–345
Merker S., Boucsein D., Feldmeyer B., Perwitasari‐Farajallah D., Streit B.
- (2013). Sexy Strangers – Acoustic mate recognition in a tarsier hybrid zone. International Prosimian Conference 2013, Ranomafana, Madagascar
Bohr Y. E.‐M. B., Purbatrapsila A., Streit B., Merker S.
- (2014) Control Region Length Dynamics Potentially Drives Amino Acid Evolution in Tarsier Mitochondrial Genomes. Journal of Molecular Evolution 79:40‐51
Merker S., Thomas S., Voelker E., Perwitasari‐Farajallah D., Feldmeyer B., Streit B. & Pfenninger M.
(See online at https://doi.org/10.1007/s00239-014-9631-2) - (2014). Dating the wrong guy – Asymmetry in a tarsier hybrid tension zone. 25th Congress of the International Primatological Society, Hanoi, Vietnam
Bohr Y. E.‐M. B., Purbatrapsila A., Streit B., Merker S.
