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Body shape for Poeciliopsis latidens and P. prolifica for the different number of competitors (0, 1, and 21). Thin-plate spline grids are shown at a scale of 3#, with lines connecting landmarks added to assist interpretation.
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Competition has long been recognized as a central force in shaping evolution, particularly through character displacement. Yet research on character displacement is biased, as it has focused almost exclusively on pairs of interacting species while ignoring multispecies interactions. Communities are seldom so simple that only pairs of species intera...
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Context 1
... ( fig. 3). Both species are less similar to each other in shape in allopatry (MD 0 p 0:0422, P ! :0001) than when they co-occur with competitors (MD 1 p 0:0192, P p :7989; MD 21 p 0:0223, P p :2193). Overall, the body shape of both P. prolifica and P. latidens when they cooccurred with other species was less streamlined and more robust ( fig. 4) than when they occurred alone. However, some differences in body shape depended on whether they co-occurred with one competitor or with two or more competitors (fig. 4). When P. prolifica and P. latidens cooccurred with one competitor, they had a more robust shape with a deep belly, a more dorsally oriented mouth, and a smaller head ...
Context 2
... P p :7989; MD 21 p 0:0223, P p :2193). Overall, the body shape of both P. prolifica and P. latidens when they cooccurred with other species was less streamlined and more robust ( fig. 4) than when they occurred alone. However, some differences in body shape depended on whether they co-occurred with one competitor or with two or more competitors (fig. 4). When P. prolifica and P. latidens cooccurred with one competitor, they had a more robust shape with a deep belly, a more dorsally oriented mouth, and a smaller head and eye compared with their allopatric shape. However, when they co-occurred with two or more competitors, the belly shape was intermediate between the shape with zero ...
Context 3
... with a deep belly, a more dorsally oriented mouth, and a smaller head and eye compared with their allopatric shape. However, when they co-occurred with two or more competitors, the belly shape was intermediate between the shape with zero competitors and the shape with one competitor, but the eye was larger than that of the allopatric shape ( fig. ...
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... Specifically, the hypothesis of interest is whether shape differs between species or locations on at least some relative warps (i.e., shape variables). This vectorization of the multivariate response variables allows parametric testing of multiple and complex interaction effects and has been used successfully to test for shape variation in a variety of systems, among populations, and species [5,22,23,[30][31][32][33][34]36]. We estimated degrees of freedom using the Kenward and Roger method [37]. ...
... This clear divergence in somatic shape between sister species suggests a mechanism of ecological character displacement [43]. Character displacement occurs when species in sympatry experience divergence of one or more characters in response to interspecific competition [36,44]. Selection for reduced competitive overlap can drive the ecological and accompanying morphological divergence in regions where the species are sympatric [45,46]. ...
Species delimitation can be based on the consideration of several different criteria, including the differentiation of ecological or functional traits. Two species of Pacific rockfish, the dark rockfish (Sebastes ciliatus) and the dusky rockfish (Sebastes variabilis), appear to represent recently divergent evolutionary lineages. We evaluate evidence for the differentiation of these two species in somatic shape using geometric morphometrics at two locations in the northeast Pacific where they occur in sympatry. The somatic shape was significantly different between species, but the species’ shape did not vary between the two locations. Sebastes ciliatus had an upturned and relatively smaller head, eye, and jaw, and an elongated midbody, whereas S. variabilis had a downturned and larger head, eye, and jaw, and a shorter midbody. These results suggest that S. ciliatus and S. variabilis are morphometrically differentiated in a similar way in both locations. The somatic shape differentiation between these two sympatric species is similar to genus-wide patterns of somatic shape differentiation.
... Available empirical evidence suggests that RCD plays an important role in the evolution of diversity (Pfennig and Pfennig 2005;Schluter 2000). This mechanism has been reported in diverse organisms, including insects (Brown and Wilson 1956;Walker 1974;Kawano 2002), fishes Schluter 2000; Crampton et al. 2011;Roth-Monzón et al. 2020), birds (Brown and Wilson 1956;Diamond et al. 1989;Seddon and Tobias 2010), reptiles (Melville 2002;Dayan and Simberloff 2005) and amphibians (Brown and Wilson 1956;Johanet et al. 2009). ...
Reproductive Character Displacement (RCD) refers to the phenomenon of greater differences in reproductive characters between two species when they occur in sympatry compared to when they occur in allopatry to prevent maladaptive hybridization. We explored whether reinforcement of a mechanical barrier involved in the first contact point between male and female genital traits during copulation in the cross between Ischnura graellsii males and Ischnura elegans females has led to RCD, and whether it supports the lock-and-key hypothesis of genital evolution. We employed geometric morphometrics to analyze the shape and size of male and female genital traits, controlling for environmental and geographic factors. Consistent with an increase in mechanical isolation via reinforcement, we detected larger divergence in genital traits between the species in sympatry than in allopatry, and also stronger signal in females than in males. In the Northwest (NW) hybrid zone, we detected RCD in I. graellsii males and I. elegans females, while in the Northcentral (NC) hybrid zone we detected RCD only in I. elegans females and I. elegans males. The detection of RCD in both sexes of I. elegans was consistent with the lock-and-key hypothesis of genital evolution via female choice for conspecific males in this species. Our study highlights the importance of using geometric morphometrics to deal with the complexity of female reproductive structures while controlling for environmental and geographic factors to investigate RCD. This study contributes valuable insights into the dynamics of reproductive isolation mechanisms and genital coevolution.
... 82 We also excluded relative warps that individually accounted for < 1% of shape variation to avoid inflating the real degrees of freedom associated with analysis of shape variation. [82][83][84] We ran a multivariate linear mixed model to analyze shape change in the head and premaxilla during development in the sucker lineages. [82][83][84][85][86][87][88] We analyzed head and premaxilla shape separately, using relative warps as the response variable. ...
... [82][83][84] We ran a multivariate linear mixed model to analyze shape change in the head and premaxilla during development in the sucker lineages. [82][83][84][85][86][87][88] We analyzed head and premaxilla shape separately, using relative warps as the response variable. The multivariate linear mixed model requires a univariate response variable, so we vectorized the matrix of relative warps so each individual specimen was represented by 9 rows (head) and 6 rows (premaxilla) of data. ...
... The index variable preserved the order of the relative warps so that comparisons were made across matching relative warps between lineages. [82][83][84][85] Explanatory variables in our model included: lineage (discrete predictor; three values), week (discrete predictor; 15 values for head shape; 6 values for premaxilla shape, described below), the index variable, the interactions between the main effects and the index variable and the three-way interaction between lineage, week, and the index variable. We did not include centroid size (multivariate measure of shape derived from analysis in tpsRelW) as a covariate in our analyses because week acted as an index for stage of development and size. ...
Heterochrony—alteration to the rate or timing of development—is an important mechanism of trait differentiation associated with speciation. Heterochrony may explain the morphological divergence between two polyploid species, June sucker (Chasmistes liorus) and Utah sucker (Catostomus ardens). The larvae of both species have terminal mouths; however, as adults, June sucker and Utah sucker develop subterminal and ventral mouths, respectively. We document a difference in the timing of shape development and a corresponding change in the timing of gene expression, suggesting the distinctive mouth morphology in June suckers may result from paedomorphosis. Specifically, adult June suckers exhibit an intermediate mouth morphology between the larval (terminal) and ancestral (ventral) states. Endemic and sympatric Chasmistes/Catostomus pairs in two other lakes also are morphologically divergent, but genetically similar. These species pairs could have resulted from the differential expression of genes and corresponding divergence in trait development. Paedomorphosis may lead to adaptive diversification in Catostomids.
... These relative warps in combination were used as shape variables (i.e. the response variable) in subsequent analyses. To account for the unidimensional nature of sliding semilandmarks and to avoid inflating the true degrees of freedom, we did not use relative warps that accounted for < 1% of shape variation (Williams et al. 2017, Roth-Monzón et al. 2020). Thus, we used the first nine relative warps as response variables to characterize bill shape, which combined accounted for 99.6% of all shape variation. ...
... The predictor variables were sex, island/mainland, and an index variable used to preserve the order of relative warps (nine levels for the nine relative warps, e.g. Roth-Monzón et al. 2020, Searle et al. 2021. The index variable preserved the order of the relative warps such that comparisons between groups (e.g. ...
... Because relative warps are principal components, they have a mean of 0; more importantly, they have an arbitrary ordination. Thus, a single individual may have a positive score on some relative warps and a negative score on other relative warps so that their mean score across all relative warps may be near 0. It was only by matching relative warps in the same order (by using the index variable as a predictor) that we could accurately test the hypothesis of interest (Wesner et al. 2011, Hassell et al. 2012, Ingley et al. 2014, Roth-Monzón et al. 2020, Searle et al. 2021. We included sex and the sex by index variable interaction to see if the well-documented sexual size dimorphism included a shape effect. ...
Feeding morphology permits animals to adapt to changing environments and is often under strong selection. We evaluated if bill shape varies according to differences in dietary prey taken across geographical ranges (North America, Central America, South America, and Caribbean islands) in a ubiquitous, New World raptor species, the American kestrel (Falco sparverius). Specifically, we predicted that bills in geographies where kestrels consumed a larger proportion of vertebrates would be shorter and wider, with a larger tomial tooth. We reviewed the literature on kestrel diets across their range and quantified potential differences in bill shape using geometric morphometric methods for 245 museum specimens. The literature review revealed that most prey consumed by kestrels in North, South, and Central America were invertebrates (51.6–69.1%), whereas Caribbean kestrels consumed mostly vertebrates (61.4%), most of which were reptiles (77.3%). Morphometric analyses agreed with these findings; bill shape differed for island versus mainland kestrels but not among mainland regions. Bill shape on islands reflected a more robust bill with a larger tomial tooth, but had a longer hook, which we suggest is adaptive for consumption of lizard prey, more available on islands due to reduced competition with other raptors compared to mainland regions.
... Because relative warps are principal components, they have a mean of 0; and more importantly, they have an arbitrary ordination. Thus, a single individual may have a positive score on some relative warps and a negative score on other relative warps so that their mean score across all relative warps may be near 0. It was only by matching relative warps in the same order (by using the index variable as a predictor) that we could accurately test the hypothesis of interest (Hassell et al., 2012;Ingley et al., 2014;Roth-Monzón et al., 2020;Searle et al., 2021;Wesner et al., 2011). We estimated degrees of freedom using the Kenward and Roger method (1997). ...
Livebearing fishes are a common model for studying the effects of predation on prey biology. Numerous studies have found differences in life history, sexual selection, behavior, and morphology between populations of the same species that co‐occur with predators and those that do not. Alfaro cultratus is a livebearing fish with populations in different predation environments, but unlike other livebearers, this species also has an extreme body shape that is laterally compressed. Given this unusual morphology, we asked if predation environment would still predict overall body shape, as has been documented in other species. We collected specimens from both predator and no predator sites in Costa Rica and used a geometric morphometrics analysis to determine if body shape is affected by predation environment, while controlling for size and river gradient. Body shape does indeed differ between predation environments; however, the observed differences contrast with the patterns found in other livebearer systems. Alfaro cultratus in predation environments had deeper and shorter bodies and deeper caudal peduncles than those found in environments without dominant fish predators.
... We used the first six of these relative warps, which accounted for 99.89% of total shape variation, for additional analysis, and excluded four relative warps that accounted for less than 0.5% of variation. Excluding these relative warps allowed us to avoid inflating the degrees of freedom in our shape analysis [28,29]. ...
... We used a multivariate linear mixed model to evaluate the effects of morph (sinistral or dextral), centroid size (a measure of size commonly used in geometric morphometrics) [30], and locality on shape variation [28,29]. In each analysis, we used relative warps (shape variables) as our response variable. ...
Antisymmetry is a striking, yet puzzling form of biological asymmetry. The livebearing fish Xenophallus umbratilis exhibits antisymmetry in the male intromittent organ and provides a system that is well-suited for studying the nature of variation in antisymmetrical traits. Using geometric morphometrics, we test the hypothesis that because the gonopodium is critical to fitness there will not be significant differences in gonopodium shape between the two gonopodial morphs in this species. Our results are consistent with this prediction, though we found that gonopodium shape differed with gonopodium size.
... Acknowledging the synergy between these two disciplines, this approach has led to widespread usage of the 'multispecies' descriptor (e.g. Bittleston et al., 2016;Roth-Monzón et al., 2020) to refer to aspects of ecological networks which, in turn, has led to significant breakthroughs in our understanding of how biotic interactions influence evolutionary processes and affect biodiversity. For instance, experiments by Betts et al. (2018) found that bacterial hosts exhibited a higher rate of molecular evolution and diversification when exposed to a greater diversity of viral parasites; and Woodward et al. (2012) showed how climate change can alter the structure and composition of food webs, with larger and rarer species being disproportionately affected. ...
... Finally, by drawing on insights gained from other fields that have advanced our understanding of multispecies interactions (e.g. Betts et al., 2018;Bramon Mora et al., 2020;Roth-Monzón et al., 2020), we discuss potential opportunities to use brood parasitism as a model system for studying multispecies interactions. ...
The relationships between avian brood parasites and their hosts are widely recognised as model systems for studying coevolution. However, while most brood parasites are known to parasitise multiple species of host and hosts are often subject to parasitism by multiple brood parasite species, the examination of multispecies interactions remains rare. Here, we compile data on all known brood parasite–host relationships and find that complex brood parasite–host systems, where multiple species of brood parasites and hosts coexist and interact, are globally commonplace. By examining patterns of past research, we outline the disparity between patterns of network complexity and past research emphases and discuss factors that may be associated with these patterns. Drawing on insights gained from other systems that have embraced a multispecies framework, we highlight the potential benefits of considering brood parasite–host interactions as ecological networks and brood parasitism as a model system for studying multispecies interactions. Overall, our results provide new insights into the diversity of these relationships, highlight the stark mismatch between past research efforts and global patterns of network complexity, and draw attention to the opportunities that more complex arrangements offer for examining how species interactions shape global patterns of biodiversity.
... In addition, we used centroid size (a multivariate measure of size) derived from this analysis to represent the stage of ontogenetic development. We excluded relative warps that individually accounted for < 1% of shape variation to avoid inflating the real degrees of freedom associated with analysis of shape variation [17,74]. Consequently, we used the first 12 of 22 relative warps for the body (accounting for 96.15% of total shape variation) and the first 9 of 10 relative warps for the head (accounting for 99.91% of total shape variation). ...
... To determine the effects of velocity environment and ontogeny on shape variation in T. areolatus, we used a multivariate linear mixed model [16,17,74]. We analyzed body and head shape separately, using relative warps as the response variable. ...
... We included the interaction between velocity environment and centroid size (ontogeny) to test for different patterns of shape variation across ontogeny between velocity environments. The multivariate linear mixed model required that the matrix of shape variables (relative warps) be vectorized such that each individual specimen was represented by 12 rows (body) or 9 rows (head) of data, and each row corresponded to one relative warp [74]. Thus, the response variable is transposed from a row in a matrix to a vector column of responses. ...
Body and head shape among fishes both vary between environments influenced by water velocity and across ontogeny. Although the shape changes associated with variation in average water velocity and ontogeny are well documented, few studies have tested for the interaction between these two variables (i.e., does ontogenetic shape variation differ between velocity environments). We use geometric morphometrics to characterize shape differences in Trichomycterus areolatus, a freshwater catfish found in high and low-velocity environments in Chile. We identify a significant interaction between velocity environment and body size (i.e., ontogeny). Ontogenetic patterns of shape change are consistent with other studies, but velocity environment differentially affects the ontogenetic trajectory of shape development in T. areolatus. Shape change over ontogeny appears more constrained in high-velocity environments compared to low-velocity environments.
... change in different single traits or in combinations of traits) across communities (Losos 2011;Germain et al. 2017), and determine when species interactions lead to shifts in correlated or independently-evolving traits. Second, while most studies of character displacement have focused on pairwise interactions (but see Lemmon and Lemmon 2010;Miller et al. 2014a;Grant 2017;Roth-Monzon et al. 2020), many species exist in complex ecological communities, where interactions with multiple species could include indirect and higher-order interactions This is the author's accepted manuscript without copyediting, formatting, or final corrections. It will be published in its final form in an upcoming issue of The American Naturalist, published by The University of Chicago Press. ...
AbstractA current frontier of character displacement research is to determine whether displacement occurs via multiple phenotypic pathways and varies across communities with different species compositions. Here, we conducted the first test for context-dependent character displacement in multimodal floral signals by analyzing variation in floral scent in a system that exhibits character displacement in flower size and that has multiple types of sympatric communities. In a greenhouse common garden experiment, we measured quantitative variation in volatile emission rates of the progeny of two species of Clarkia from replicated parental communities that contain one, two, or four Clarkia species. The first two axes of a constrained correspondence analysis, which explained 24% of the total variation in floral scent, separated the species and community types. Of the 23 compounds that were significantly correlated with these axes, nine showed patterns consistent with character displacement. Two compounds produced primarily by C. unguiculata and two compounds produced primarily by C. cylindrica were emitted in higher amounts in sympatry. Character displacement in some volatiles varied across sympatric parental communities and occurred in parallel with displacement in flower size, demonstrating that this evolutionary process can be context dependent and may occur through multiple pathways.
... Since relative warps are principal components, they have a mean of 0; more importantly, they have an arbitrary ordination. Thus, a single individual may have a positive score on some relative warps and a negative score on other relative warps so that their mean score across all relative warps may be near 0. It was only by matching relative warps in the same order (by using the index variable as a predictor) that we could accurately test the hypothesis of interest [50]. ...
... We included location as a random effect in our model to adjust for the variation that is inherent to a natural experiment, including the variation along the latitudinal gradient and between drainage basins. This allowed us to test for a general morphometric response to lake colonization [50]. Degrees of freedom were estimated using the Kenward-Roger method [51]. ...
Body and head shape in fish responds to environmental factors such as water flow rate, food sources, and niche availability. However, the way in which fish respond to these environmental factors varies. In Central Chile, multiple river and lake systems along the coast provide an ideal study site to investigate these types of shape changes. We use geometric morphometrics to characterize shape differences in Galaxias maculatus (Jenyns) between river and lake populations. Lake fish converge on a shape with a more fusiform body, narrower head, and larger eyes, while river fish have a more robust body, rounder head, and smaller eyes. These shape changes are consistent with a shift to zooplanktivorous foraging in lakes, as evidenced in other systems. Unlike some fish species that develop polymorphisms in body shape after colonization (e.g., benthic and limnetic forms), G. maculatus in lakes exhibit a monomorphic limnetic form.
