Dr Tigga Kingston

Assistant Professor

Evolutionary Ecology

Until recently, the limited fossil record and incomplete phylogenies have obscured the origins of the extraordinary taxonomic and ecological diversity of bats, but more recent work suggests that a rapid radiation (one unprecedented in mammalian history) occurred in the Eocene, precipitated by an explosive increase in insect diversity. The lineage leading to bats was uniquely placed to exploit this new resource because of two specializations that distinguish them from all other land mammals: flight and echolocation.

 

In particular, the study of echolocation is a central component of my research into the origins and diversification of Old World bats; it has provided insights into mechanisms of resource partitioning (Kingston et al. 1999, J. Zool., 249:359-374, Kingston et al. 2000, Oecologia, 124:332-342), and communication and social biology (Kingston et al. 2000, Bioacoustics, 11:1-16) that are proving pivotal in determining the speciation mechanisms behind key Old World radiations (Kingston et al. 2001, Proc. R. Soc., 268:1381-1386; Kingston & Rossiter 2004, Nature, 429; 654–657; Thabah et al. in press Biol. J. Linn. Soc.).

 

My current research focuses on two contrasting systems from Sulawesi and Malaysia. In Sulawesi, the large-eared horseshoe bat (Rhinolophus philippinensis) occurs as three distinct, sympatric size morphs that echolocate at different frequencies, corresponding to alternate harmonics of the same fundamental frequency (Kingston & Rossiter 2004, Nature 429; 654–657). These morphs have undergone recent genetic divergence and we suggested that harmonic-hopping creates a discontinuity in the bats’ perception of available prey that can initiate disruptive selection. Since call frequency in horseshoe bats plays a dual role in resource acquisition and communication, ecological selection on frequency may lead to assortative mating and ultimately reproductive isolation, even in the absence of external barriers to gene flow.  It seems that this process has occurred in parallel more than once, with a second pair of sympatric size morphs occurring in Northeast Australia. The two Australian morphs call at the same frequencies as the Sulawesi morphs, but are genetically more related to one another than to their Indonesian counterparts.   However, despite the widespread range of this species, SE Sulawesi and NE Australia remain the only two localities with sympatric size morphs for which acoustic data are available. Future work will determine the acoustic and genetic relationships of morphs throughout their range; will test the exact role of call frequency in prey identification and communication; and investigate the proximate mechanisms by which these frequency shifts could come about (cochlear, laryngeal and nasopharyngeal morphology/physiology).

 

In contrast, I identified two Hipposideros species from Malaysia that are morphologically cryptic but genetically and acoustically divergent. In this instance, the call frequency differences are unlikely to effect any ecological segregation, but may be the consequence of social selection for a clear communication channel (Kingston et al. 2001, Proc. R. Soc., 268:1381-1386). The phylogeography, ecology and social biology of these species are now the subject of a PhD dissertation (Susan Murray, Boston University).  Similarly, differences in echolocation call frequency among populations of Hipposideros larvatus throughout Indo-Malaya do not reflect phylogenetic relationships (Thabah et al. 2006, Biol. J. Linn.), indicating that call frequency is a poor indicator of evolutionary history. Instead, divergence in call frequency in this system probably occurs randomly in isolation, possibly augmented by character displacement on secondary contact to facilitate intra-specific communication.

 

These studies suggest that, at low echolocation frequencies, harmonic hopping can initiate major divergence events. However, subsequent branching of populations using higher call frequencies is more likely to occur through isolation (drift) or social selection. In collaboration with Stephen Rossiter (Queen Mary, University of London), I am currently investigating the acoustic and genetic differentiation of allopatric populations of Rhinolophus and Hipposideros species distributed across a chain of isolated islands (Wakatobi) off the coast of SE Sulawesi. Preliminary analyses of five years of data suggest that the direction of change in call frequency across islands is not consistent across species, indicating a role for social selection and/or drift.

Kerivoula pellucida

Rhinolophus macrotis

Mops mops

Rhinolophus lepidus