MORPHOLOGICAL VARIATION IN THE LIMBS OF TARICHA GRANULOSA (CAUDATA: SALAMANDRIDAE): EVOLUTIONARY AND PHYLOGENETIC IMPLICATIONS

Abstract

Abstract.-Variation in the limb skeleton was studied in a large sample (452 individuals) of adult newts (Taricha granulosa) from a single population in central California. A standard morphology is found in the hands and feet in more than 70% of individuals, but there is important variation in the remainder of the sample. Although twice as many individuals express variant tarsal (18.9%) than carpal (9.3%) patterns, the carpus reveals a greater diversity of variant conditions. Only a few of the many possible arrangements (including loss, addition, and amalgamation) of the seven carpal and nine tarsal elements are encountered. Most of the observed patterns are readily classified on the basis of phylogenetic relationship and models of development. Five patterns are bilaterally symmetrical. Two of these five arrangements are atavisms that represent plesiomorphic states. The other three symmetrical variants duplicate patterns found elsewhere among derived urodele taxa. These homoplastic patterns correspond to apomorphies of other genera within the same family or apomorphies of deeply nested and highly specialized members of other families (e.g., several plethodontid genera). This variation reveals the potential of the generative system and suggests the existence of limited domains of phenotypic expression. Both the origin of novelty and the restoration of ancestral states reflect the action of design constraints that not only place limits but also provide opportunities during the morphologic and phyletic diversification of urodeles.Key words.-Atavism, caudata, constraint, homoplasy, limbs, variation.Received October 4, 1993. Accepted August 3, 1994.The constraints imposed by phylogenetic history and embryological development can lend a predictability to patterns of intraspecific variation. The parallels between synapomorphies, intrapopulational variability, and experimentally induced teratologies reflect the influence of internal constraints on variation (Alberch 1983; Hanken 1985;Maynard Smith et al. 1985; Wagner 1989a,b; Vogl and Rienesl1991;Rienesl and Wagner 1992). The high frequency of atavistic morphologies in vertebrate phylogenies suggests that phylogenetic relationships can be one means of predicting patterns of intraspecific variation (Hall 1984;Wake 1991). The congruence between predictions from models of development and observations of phenotypic diversity directs attention to specific mechanisms that are involved in the generation of patterns of intraspecific variation and, by extension, morphological novelties.The limb morphology of urodele amphibians has emerged as a promising system for analysis of the action of internal constraints on morphological diversity (Alberch

Competition among body parts in the development and evolution of insect morphology

“…Yet despite a long history of interest in this problem, empirical studies that demonstrate how development biases the generation of morphological variation are rare (7)(8)(9)(10)(11), and empirical links between developmental phenomena and genetic constraints on evolution are all but nonexistent (12)(13)(14). Herein we demonstrate one way in which development may limit the generation of morphological variation, namely, through a common developmental environment within the organism that imposes resource allocation tradeoffs among growing body parts.…”

Why five fingers? Evolutionary constraints on digit numbers

“…Variation, including intraspecific variation in the number of phalanges, is more common in amphibians than in aroniotes [50][51][52][53][54] . Variation in the number of carpal and tarsal bones is also remarkably high [50][51][52][53][54][55] . In particular, hyperphalangy occurs frequently, and this represents the only common form of evolutionary reversal of limb reduction.…”

Macroevolutionary patterns of defense and pollination inDalechampiavines: Adaptation, exaptation, and evolutionary novelty

“…Other historically contingent evolutionary scenarios include consistent sequences of trait change (''ordered change'') (18); exaptation (13) (e.g., coopting preexisting compounds for new defense or reward functions); and evolutionary ''novelty'' through regulatory gene-based trait reversals (''atavisms'') (19)(20)(21). Previous macroevolutionary studies of plant-herbivore interactions have shown patterns of escalation and decline in the intensity and effectiveness of different defense systems (22)(23)(24) and specific sequences of evolutionary change in plant defense systems (25,26).…”