Geographic dialects in blind mole rats: role of vocal communication in active speciation.

Abstract

We compared and contrasted the physical structure of male "courtship" calls of 59 subterranean mole rats belonging to the Spalax ehrenbergi superspecies in Israel, comprising 11 populations of four chromosomal species (2N = 52, 54, 58, and 60). We also conducted behavioral auditory discrimination tests of 144 females of the four species in the laboratory. The results indicate that each chromosomal species has a vocal dialect significantly different from all others, although the call of ZN = 60, the last derivative of speciation,is not yet fully differentiated. Females of 2N = 52, 54, and 58 preferred their homospecific mates' calls, whereas females of 2N = 60 did not. We conclude that call differentiation builds up gradually and provides an efficient ethological reproductive premating isolation mechanism between the emerging species in the active speciation of mole rats in Israel.Speciation is a key problem of evolution (1, 2). Yet, despite numerous studies (reviewed in refs. 1-7), its modes, genetics, and mechanisms remain little known and highly hypothetical (e.g., refs. 7 and 8). To unveil the course of speciation events, studies must be conducted in cases of active speciation (9). The crux of speciation is the development of reproductive isolation between populations, followed by ecological compatibility of the emerging species. Reproductive isolation may be attained by either premating or postmating isolation mechanisms, or both (1-7). The role of vocal communication as a premating isolation mechanism in animal speciation has been reviewed (1, 2). Specific examples are Drosophila (10), arthropods (11), orthopterans (12), spiders (13), frogs (14, 15), birds (16, 17), and mammals (18).We analyzed the existence of geographic dialects in the "courtship" calls of blind subterranean mammals of the Spalax ehrenbergi superspecies in Israel. We also tested, in the laboratory by female discrimination experiments, the function of the vocal dialects as a premating ethological isolation mechanism. This was done in an attempt to highlight the evolutionary significance and rate of the build-up of reproductive isolation, and hence of speciation, in this case of active speciation (19)(20)(21)(22)(23).Subterranean mole rats in Israel, belonging to the S. ehrenbergi superspecies, involve four morphologically indistinguishable, homozygous chromosomal species (19) with 2N = 52, 54, 58, and 60. Multidisciplinary studies (reviewed in refs. 20-23) provide telling evidence of both the evolutionary dynamics and the various stages of speciation of the complex. The evolution of S. ehrenbergi is intimately associated with the climatic and biotic differentiation of Israel. The chromosomal species inhabit extensive regions, which are distributed clinally and parapatrically along a southward gradient of increasing aridity. Their distribution is correlated with four climatic regimes: 2N = 52, cool and humid; 2N = 54, cool and dry; 2N = 58, warm and humid; and 2N = 60, warm and dry (see figure 1 in ref. 21).The "courtship" call of ...

Distributional Limits and Melanism in the South-West of the Range of the Crowned Sifaka (Propithecus coronatus), Madagascar

“…The importance of signals for the evolution and diversification of taxa has been suggested in many species (Mayr 1963;Ryan and Rand 1999;Grant and Grant 2006;Robillard et al 2006). On the one hand, speciesspecific signals can be considered a result of sexual selection in which they function as a premating isolation mechanism (Mayr 1963;Nevo et al 1987). On the other hand, speciesspecific vocalizations can be a result of natural selection through adaptations of the acoustic structure of calls according to habitat properties in order to optimize their transmission (Morton 1975;Ryan et al 1990;Brown et al 1995).…”

Geographic variation in vocal signals ofCtenomys pearsoni

“…Vocal dialects have been detected in Spalax ehrenbergi but they have been described for a signal used by the species mainly in courtship or aggressive situations, and always in close contact (Nevo et al 1987). In this case, the authors have correctly assigned 79% of variation using discriminant analysis of four chromosomal forms with four variables (3 frequency and 1 rhythm variable).…”

“…The fact that female Spalax could discriminate different "courtship" signals is interesting. However, since signal manipulation was not performed, we cannot assume that the parameters used by Nevo et al (1987) to separate the populations by discriminant analysis are the same as used by females for male identification.…”

Seismic communication in a blind subterranean mammal: a major somatosensory mechanism in adaptive evolution underground.

“…The intensity ofthe noise was overall 10 dB higher than that of the taps. However, because of the high-frequency bias of the We have previously established in mole rats of the S. ehrenbergi superspecies the importance of vocal (14)(15)(16)(17)(18) and olfactory (13) Acute seismic sensitivity has been reported in arthropods (32), amphibians (33,34), reptiles (35), and mammals (36,37) and is quite widespread in both invertebrates and vertebrates (24). The evidence presented here supports the existence of a clear-cut somatosensory mechanism for transmitting vibrational signals directly to the brain, complementing shortdistance audition.…”

“…Olfactory communication (13) is also an important ethological reproductive isolating mechanism underlying assortative mating and enhancing speciation. Progressive evolution of short-range acoustic communication in S. ehrenbergi was described behaviorally (14), physically (15), transmissionally (16), and morphophysiologically (17,18). Species of S. ehrenbergi have a rich vocal repertoire with a main vocal energy below 1 kHz (15).…”