Pattern Of Character Displacement Research Articles

Phylogeographical analysis of character displacement in feeding phenotypes of snail-feedingAcoptolabrusground beetles

AbstractEcological character displacement predicts that interspecific resource competition results in greater trait divergence between species in sympatry than in allopatry. However, other processes, such as ecological sorting, result in the same pattern of trait variation. In this study, we characterize character displacement in eight species of snail-feeding Acoptolabrus ground beetles in the Far East. Acoptolabrus exhibit divergent feeding phenotypes, including species with a slender forebody that is able to intrude into large shells and species with stout heads and mandibles for crushing small shells. The pattern of character displacement in feeding phenotypes was confirmed by multivariate analysis of body dimensions. Molecular phylogenetic analysis, divergence time estimation and biogeographical analysis revealed that sympatry and phenotypic divergence occurred repeatedly during the Pleistocene and almost simultaneously within each geographical area. Comparative analysis revealed that the evolution of feeding phenotypes best fitted a selective model with three adaptive optima, corresponding to the three cases of sympatry with a congener. Repeated coincidences of sympatry and adaptive differentiation in feeding phenotypes suggested causal relationships, although the precise order of events was difficult to discriminate. This study provides insight into the spatiotemporal dynamics of interspecific interactions and adaptive phenotypic diversification.

Investigating opposing patterns of character displacement in release and advertisement vocalizations ofBufo fowleriandBufo americanus(Anura; Bufonidae)

Anuran release vocalizations function to prevent prolonged amplexus between males, whereas advertisement vocalizations potentially act as a premating isolation mechanism. To facilitate rapid release during heterospecific amplexus, selection should favor convergent character displacement in release vocalizations. Conversely, to promote isolation between sympatric congeners, selection should favor divergent character displacement in advertisement vocalizations. I examined properties of release and advertisement vocalizations of Bufo fowleri and Bufo americanus that are important in mate recognition (periodicity and dominant frequency) to determine if the two calls exhibit opposing patterns of character displacement. Release vocalizations showed no pattern of displacement. The periodicity of sympatric advertisement vocalizations differed from that of allopatric vocalizations for B. americanus but not for B. fowleri. However, the results were not consistent with the pattern expected for divergent character displacement because the two species differed in this parameter in allopatry. These results are compared with published reports of char acter displacement in the B. americanus species-group in the context of a possible mosaic hybrid zone for these species.

Investigating opposing patterns of character displacement in release and advertisement vocalizations of <i>Bufo fowleri</i> and <i>Bufo americanus</i> (Anura; Bufonidae)

Investigating opposing patterns of character displacement in release and advertisement vocalizations of <i>Bufo fowleri</i> and <i>Bufo americanus</i> (Anura; Bufonidae)

Shape Divergence Associated with Size Convergence in Sympatric East African Jackals

The geographic ranges of three extant species of medium—sized canid, the sidestriped (Canis adustus), the golden (C. aureus), and the blackbacked (C. mesomelas) jackal, overlap only in East Africa. Elsewhere each species exists alone or in sympatry with one other jackal species. The fossil record suggests that the golden jackal evolved outside of Africa and joined the other two species in East Africa within the last 500 000 yr. Previous research showed that unlike other sympatric canids, all three jackal species in East Africa are extremely similar in size and overall morphology and thus exhibit no obvious evidence of ecological character displacement. Moreover, the three species do not form a monophyletic group, are distantly related, and thus may have had ample time to diverge morphologically. Here, we explore in further detail the possibility of character displacement in the three species by assessing variation in 62 measures of the skull and teeth for populations of all three species throughout their ranges. The expanded measurement and population sample allows us to explore four possible manifestations of character displacement: (1) divergence in size, (2) divergence in shape, (3) reduced morphological variability, and (4) reduced sexual dimorphism. There is no evidence of size divergence among jackals in East Africa; by contrast the three species appear to converge on a similar size. However, divergence in shape is apparent. The recent insinuation of golden jackals into the East African fauna has resulted in character divergence and probable niche compression of blackbacked jackals as evidenced by adaptations for increased carnivory, reduced sexual dimorphism, and reduced variability. The response has been asymmetric as the golden and sidestriped jackals have not diverged functionally or shown niche compression. The pattern of character displacement is likely a function of starting conditions at the time the three became sympatric. The golden jackal exhibits dietary adaptations intermediate to those of the other two species but more similar to those of blackbacked jackal. Thus character displacement was more likely to occur in goldens and blackbacks. Selection for increased carnivory in the blackbacked jackal might have been favored because of the abundance of vertebrate prey in the East African plains. The success of the golden jackal as an insinuator into East Africa suggests that the carnivore guild might not be saturated.