Ecological divergence and talar morphology in gorillas

Gorillas occupy a variety of habitats from the west coast to eastern central Africa. These habitats differ considerably in altitude, which has a pronounced effect on forest ecology. Although all gorillas are obligate terrestrial knuckle‐walking quadrupeds, those that live in lowland habitats eat fruits and climb more often than do those living in highland habitats. Here we test the hypothesis that gorilla talus morphology falls along a morphocline that tracks locomotor function related to a more inverted or everted foot set. This proposed morphocline predicts that gorillas living in lowland habitats may have a talocrural joint configured to facilitate a more medially oriented foot during climbing, suggesting that they may be more adaptively committed to arboreality than gorillas living in highland habitats. To quantify the relative set of the foot in gorillas, we chose two three‐dimensional measurements of the talocrural joint: mediolateral curvature of the trochlea and relative surface area of the lateral malleolus. Our results show that, in comparison to their eastern counterparts, western gorillas have talar features that reflect a more medially directed sole of the foot. This morphology likely facilitates foot placement in a wider range of positions and minimization of shearing stresses across the joint when the foot is loaded on more curved or vertically oriented substrates as occurs during climbing and other arboreal behaviors. In contrast, eastern gorilla talar morphology is consistent with habitual placement of the foot with the sole directed more inferiorly, suggesting more effective loading during plantigrade push‐off on terrestrial substrates. Am J Phys Anthropol 153:526–541, 2014. © 2013 Wiley Periodicals, Inc.     

Behavioral evaluation of exhibit modifications designed to accommodate an aged diana monkey

Modifications in a zoo exhibit were made to increase the arboreality of an aged female diana monkey, and to increase her use of the central portion of the exhibit where a new food shelf had been added. Branches, which formed ramps to this shelf, also were added. Following these changes, the aged female's arboreality increased slightly, and her use of the central portion of the exhibit increased significantly. Changes in habitat use following these modifications also were noted in the other two diana monkeys in the group. These results suggest that zoo habitats can be made more usable for individuals whose behavioral capabilities might be limited due to age or physical disability.     

Of stones and monkeys: testing ecological constraints on stone handling, a behavioral tradition in Japanese macaques

Japanese macaques are known to manipulate stones by displaying various seemingly functionless behavioral patterns, including carrying a stone, rubbing two stones together, or gathering several stones into a pile. This form of solitary object play called stone handling (SH) is a behavioral tradition in Japanese macaques, showing striking intertroop differences in frequency and form. Here, we evaluated two ecologically based hypotheses invoked to account for these differences. We hypothesized that the occurrence and form of SH would be affected by stone availability and the degree of terrestriality. We used standardized sampling methods to assess differences in SH and terrestriality among four captive and six free-ranging troops of Japanese macaques, and determine site-specific stone availability. Although we demonstrated that SH is almost exclusively a terrestrial activity, our comparative analyses showed that the number of stones readily available and the relative amount of time spent on the ground by the macaques were not associated with the intertroop differences in the occurrence of SH. Failure to accept the terrestriality and stone availability hypotheses suggests that the performance of SH and the motivation to engage in this activity are both more diverse and more complex than the direct links to time spent on the ground or the number of stones locally available. Other environmental influences and sociodemographic factors should be jointly considered to identify the sources of variation in SH, as a beginning to better understand the constraints on the appearance and subsequent diffusion of stone-use traditions in nonhuman primates. Am J Phys Anthropol, 2008. (c) 2007 Wiley-Liss, Inc.     

Ecological divergence and sexual selection drive sexual size dimorphism in new world pitvipers (Serpentes: Viperidae)

Hypotheses for the origin and maintenance of sexual size dimorphism (SSD) fall into three primary categories: (i) sexual selection on male size, (ii) fecundity selection on female size and (iii) ecological selection for gender‐specific niche divergence. We investigate the impact of these forces on SSD evolution in New World pitvipers (Crotalinae). We constructed a phylogeny from up to eight genes (seven mitochondrial, one nuclear) for 104 species of NW crotalines. We gathered morphological and ecological data for 82 species for comparative analyses. There is a strong signal of sexual selection on male size driving SSD, but less evidence for fecundity selection on female size across lineages. No support was found for allometric scaling of SSD (Rensch's rule), nor for directional selection for increasing male size (the Fairbairn–Preziosi hypothesis) in NW crotalines. Interestingly, arboreal lineages experience higher rates of SSD evolution and a pronounced shift to female‐biased dimorphism. This suggests that fecundity selection on arboreal females exaggerates ecologically mediated dimorphism, whereas sexual selection drives male size in terrestrial lineages. We find that increasing SSD in both directions (male‐ and female‐biased) decreases speciation rates. In NW crotalines, it appears that increasing magnitudes of ecologically mediated SSD reduce rates of speciation, as divergence accumulates within species among sexes, reducing adaptive divergence between populations leading to speciation.     

Genetic and morphological divergence among sympatric canids

Numerous studies have suggested that the extent of character divergence observed between two sympatric species reflects the intensity of competition for resources or space. However, the influence of time on divergence is often overlooked. We examined the relationship between time and character divergence in two groups of congeneric, sympatric canids on two continents: South American foxes and African jackals. Character divergence was assessed from measurements of body mass and dental and cranial shape. Divergence time was estimated from data on mitochondrial DNA restriction site polymorphisms. Our findings indicate that African jackals are morphologically similar despite having diverged more than 2 million years ago. By contrast, South American foxes differ substantially in both size and morphology after only 250,000 years of evolution. Thus, the lack of character divergence among the African jackals cannot be explained as a result of very recent common ancestry.     

Local ecological divergence of two closely related stag beetles based on genetic,morphological, and environmental analyses

The process of phenotypic adaptation to the environments is widely recognized. However, comprehensive studies integrating phylogenetic, phenotypic, and ecological approaches to assess this process are scarce. Our study aims to assess whether local adaptation may explain intraspecific differentiation by quantifying multidimensional differences among populations in closely related lucanid species, Platycerus delicatulus and Platycerus kawadai, which are endemic saproxylic beetles in Japan. First, we determined intraspecific analysis units based on nuclear and mitochondrial gene analyses of Platycerus delicatulus and Platycerus kawadai under sympatric and allopatric conditions. Then, we compared differences in morphology and environmental niche between populations (analysis units) within species. We examined the relationship between morphology and environmental niche via geographic distance. P. kawadai was subdivided into the “No introgression” and “Introgression” populations based on mitochondrial COI gene – nuclear ITS region discordance. P. delicatulus was subdivided into “Allopatric” and “Sympatric” populations. Body length differed significantly among the populations of each species. For P. delicatulus, character displacement was suggested. For P. kawadai, the morphological difference was likely caused by geographic distance or genetic divergence rather than environmental differences. The finding showed that the observed mitochondrial–nuclear discordance is likely due to historical mitochondrial introgression following a range of expansion. Our results show that morphological variation among populations of P. delicatulus and P. kawadai reflects an ecological adaptation process based on interspecific interactions, geographic distance, or genetic divergence. Our results will deepen understanding of ecological specialization processes across the distribution and adaptation of species in natural systems.     

The genomic bases of morphological divergence and reproductive isolation driven by ecological speciation in Senecio (Asteraceae)

Ecological speciation, driven by adaptation to contrasting environments, provides an attractive opportunity to study the formation of distinct species, and the role of selection and genomic divergence in this process. Here, we focus on a particularly clear‐cut case of ecological speciation to reveal the genomic bases of reproductive isolation and morphological differences between closely related Senecio species, whose recent divergence within the last ~200 000 years was likely driven by the uplift of Mt. Etna (Sicily). These species form a hybrid zone, yet remain morphologically and ecologically distinct, despite active gene exchange. Here, we report a high‐density genetic map of the Senecio genome and map hybrid breakdown to one large and several small quantitative trait loci (QTL). Loci under diversifying selection cluster in three 5 cM regions which are characterized by a significant increase in relative (F_ST), but not absolute (d_XY), interspecific differentiation. They also correspond to some of the regions of greatest marker density, possibly corresponding to ‘cold‐spots’ of recombination, such as centromeres or chromosomal inversions. Morphological QTL for leaf and floral traits overlap these clusters. We also detected three genomic regions with significant transmission ratio distortion (TRD), possibly indicating accumulation of intrinsic genetic incompatibilities between these recently diverged species. One of the TRD regions overlapped with a cluster of high species differentiation, and another overlaps the large QTL for hybrid breakdown, indicating that divergence of these species may have occurred due to a complex interplay of ecological divergence and accumulation of intrinsic genetic incompatibilities.     

Parallel and nonparallel ecological,morphological and genetic divergence in lake–stream stickleback from a single catchment

Parallel phenotypic evolution in similar environments has been well studied in evolutionary biology; however, comparatively little is known about the influence of determinism and historical contingency on the nature, extent and generality of this divergence. Taking advantage of a novel system containing multiple lake–stream stickleback populations, we examined the extent of ecological, morphological and genetic divergence between three‐spined stickleback present in parapatric environments. Consistent with other lake–stream studies, we found a shift towards a deeper body and shorter gill rakers in stream fish. Morphological shifts were concurrent with changes in diet, indicated by both stable isotope and stomach contents analysis. Performing a multivariate test for shared and unique components of evolutionary response to the distance gradient from the lake, we found a strong signature of parallel adaptation. Nonparallel divergence was also present, attributable mainly to differences between river locations. We additionally found evidence of genetic substructuring across five lake–stream transitions, indicating that some level of reproductive isolation occurs between populations in these habitats. Strong correlations between pairwise measures of morphological, ecological and genetic distance between lake and stream populations supports the hypothesis that divergent natural selection between habitats drives adaptive divergence and reproductive isolation. Lake–stream stickleback divergence in Lough Neagh provides evidence for the deterministic role of selection and supports the hypothesis that parallel selection in similar environments may initiate parallel speciation.     

Quantitative three-dimensional shape analysis of the proximal hallucial metatarsal articular surface in Homo, Pan, Gorilla, and Hylobates

Multidimensional morphometrics is used to compare the proximal articular surface of the first metatarsal between Homo, Pan, Gorilla, Hylobates, and the hominin fossils A.L. 333-54 (A. afarensis), SKX 5017 (P. robustus), and OH 8 (H. habilis). Statistically significant differences in articular surface morphology exist between H. sapiens and the apes, and between ape groups. Ape groups are characterized by greater surface depth, an obliquely curved articular surface through the dorso-lateral and medio-plantar regions, and a wider medio-lateral surface relative to the dorso-plantar height. The OH 8 articular surface is indistinguishable from H. sapiens, while A.L. 333-54 and SKX 5017 more closely resemble the apes. P. robustus and A. afarensis exhibit ape-like oblique curvature of the articular surface.     

Genetic, morphological, and feather isotope variation of migratory willow warblers show gradual divergence in a ring

The circular distribution of the willow warbler Phylloscopus trochilus around the Baltic Sea shares many features with the classic examples of ring species; however, the system is much younger. It has previously been shown that a secondary contact zone is located in central Scandinavia, where there are narrow clines for several morphological traits coincident with a migratory divide. Here we analyse multiple traits and genes from > 1700 males captured on breeding territories at 77 sites spread around the Baltic Sea to test the following hypothesis. If the secondary contact zone in Scandinavia is a result of divergence in two allopatric refuge populations during the last glaciation, we expect to find a similar secondary contact zone somewhere else around the circular distribution. Our results show that the trait clines were wider and displaced from each other along the eastern side of the Baltic Sea. Analyses of 12 microsatellite loci confirmed that the genome is very similar between the terminal forms ( F _ST = 0). Two AFLP-derived markers filtered out from a genomic scan instead appear to be maintained by selection. These markers exhibited steep clines at the secondary contact zone in Scandinavia, but as for the phenotypic traits, had vastly different cline centres east of the Baltic Sea. The trait clines along the ring distribution outside the Scandinavian secondary contact zone thus seem to have been shaped by independent action of selection or drift during the process of postglacial colonization.     

Differential rates of morphological divergence in birds

There are more small-bodied bird species than there are large-bodied, even on a logarithmic scale. In birds this pattern, which is also found in other higher taxa, appears not to be due to neutral evolution. It has often been suggested that the skew of body size frequency distributions is the result of a relationship between body size and the net rate of speciation, but phylogenetic analyses so far have rejected the hypothesis that small-bodied species are subject to higher net rates of speciation. On the contrary, we show that there exists a relationship between body size and its own evolutionary variability: avian families of small body size show less interspecific variation in body size than large-bodied families of similar age and species richness.     

Latitudinal and ecological correlates of morphological variation in Galaxias platei (Pisces, Galaxiidae) in Patagonia

We examined the morphological variability (23 morphometric traits) among individual Galaxias platei ( N  = 380) collected from 20 postglacial lakes in the southern Andes. The lakes were chosen to cover the latitudinal range of the species in Patagonia. Diet examined for a subset of these fish ( N  = 261) collected during the summer months (January through March), differed among river basins but there were no clear latitudinal trends in the consumption of any prey type. Diet may, however, have partially shaped morphology, as pelvic measures were negatively correlated with consumption of amphipods. Substantial differentiation among populations was observed, primarily in the shape and dimensions of the head, in caudal morphology and in fin length. Our results indicate that the morphology of G. platei varies with latitude, and may be related to risk of predation and diet.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 87 , 69–82.     

Deep molecular divergence in the absence of morphological and ecological change in the Californian coastal dune endemic trapdoor spider Aptostichus simus

Aptostichus simus is a trapdoor spider endemic to the coastal dunes of central and southern California and, on morphological grounds, is recognized as a single species. Mitochondrial DNA 16S rRNA sequences demonstrate that most populations are fixed for the same haplotype and that the population haplotypes from San Diego County, Los Angeles County, Santa Rosa Island, and Monterey County are extremely divergent (6-12%), with estimated separation times ranging from 2 to 6 million years. A statistical cluster analysis of morphological features demonstrates that this genetic divergence is not reflected in anatomical features that might signify ecological differentiation among these lineages. The species status of these divergent populations of A. simus depends upon the species concept utilized. If a time-limited genealogical perspective is employed, A. simus would be separated at the base into two genetically distinct species. This study suggests that species concepts based on morphological distinctiveness, in spider groups with limited dispersal capabilities, probably underestimate true evolutionary diversity.     

Patterns of morphological variation among populations of the widespread annual killifish Nothobranchius orthonotus are independent of genetic divergence and biogeography

Populations of annual killifish of the genus Nothobranchius occur in patchily distributed temporary pools in the East African savannah. Their fragmented distribution and low dispersal ability result in highly structured genetic clustering of their populations. In this study, we examined body shape variation in a widely distributed species, Nothobranchius orthonotus with known phylogeographic structure. We tested whether genetic divergence of major mitochondrial lineages forming two candidate species is congruent with phenotypic diversification, using linear and geometric morphometry analyses of body shape in 23 wild populations. We also conducted a common‐garden experiment with two wild‐derived populations to control for the effect of local environmental conditions on body shape. We identified different allometric trajectories for different mitochondrial lineages and candidate species in both sexes. However, in a principal components analysis of population‐level body shape, the separation among mitochondrial lineages was incomplete. Higher similarity of mitochondrial lineages belonging to different candidate species than that of same candidate species prevented distinction of the two candidate species on the basis of body shape. Analysis at the individual level demonstrated that N. orthonotus express high intrapopulation variability, with major overlap among individuals from all populations. In conclusion, we suggest that N. orthonotus be considered as a single species with an extensive geographic range, strong population genetic structure and high morphological variability.     

Habitat-associated morphological divergence in two Neotropical fish species

We examined intraspecific morphological diversification between river channel and lagoon habitats for two Neotropical fish ( Bryconops caudomaculatus , Characidae; Biotodoma wavrini , Cichlidae). We hypothesized that differences between habitats (e.g. flow regime, foraging opportunities) might create selective pressures resulting in morphological divergence between conspecific populations. We collected fish from four channel-lagoon habitat pairs in the Río Cinaruco, Venezuela, and compared body morphology using geometric morphometrics. There were two aspects of divergence in both species: (1) placement of maximum body depth and (2) orientation of the mouth. For both species, maximum body depth was positioned more anteriorly (i.e. fusiform) in the river channel than in lagoons. Both species exhibited a relatively terminal mouth in lagoons compared to the channel. The mouth of B. caudomaculatus was relatively upturned, whereas the mouth of B. wavrini was relatively subterminal, in channel habitats. Observed morphological patterns are consistent with functional morphological principles suggesting adaptive divergence. We also show that spatial distance between habitats, presumably reflecting rates of population mixing, appears to have constrained diversification. For both species, morphological divergence increased with distance between habitats. Thus morphological divergence between channel and lagoon habitats apparently reflects a balance between diversification driven by natural selection, and homogenization driven by population mixing.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 80 , 689–698.     

MtDNA haplotypes, sequence divergence, and morphological variation in Gray-breasted Wood Wrens (Henichorina leucophrys) and their conservation implications

ABSTRACT.   To reveal more clearly the places that are critical for generating and sustaining species diversity, the distribution of genetic diversity is informative for conservation. Evolutionary significant units (ESUs) represent distinct lineages within a species and are defined by genetic and morphological differences. We examine morphometrics and mitochondrial DNA sequences of two coastal and three Andean populations of Gray-breasted Wood Wrens ( Henicorhina leucophrys ) in Ecuador to determine if any populations are ESUs. Coastal Wood Wrens diverged genetically by 2.4%, 3.5%, and 4.4% from Andean populations of the northwest (Bellavista), southwest (Sural-Caucha), and southeast (Romerillos), respectively. The five populations (34 individuals) exhibited nine haplotypes. Both genetic and ecological results indicate that coastal Wood Wrens found in the Colonche Hills are ESUs, as are the Andean populations. In contrast with temperate regions, where large reserves connected by corridors may be effective, preservation of biodiversity in tropical South America may require protection of more localized areas.