Meristic and Morphometric Differences in Populations of Rivulus marmoratus

Abstract

Rivulus marmoratus (Pisces: Aplocheilidae) is a small cyprinodontid found in mangroves of the western tropical Atlantic and is the only lmown self-fertilizing, hermaphroditic vertebrate. Populations normally consist of genetically diverse groups of homozygous clones. Rivulus marmorahts has the widest range of any member of the genus (southern Brazil to central Florida) and is the only marine representative of the genus. There has been considerable speculation about the "origin" of the species in an otherwise sexually reproducing genus and family. Although well studied in the laboratory, few specimens have been collected from the wild until recently. This study examined meristic and morphometric differences among 12 widespread populations and among individual clonal lineages reared in the laboratory. Thirty-two meristic and morphometric characters in 187 fish (ranging from Brazil to Florida) were examined with univariate and multivariate statistics for determination of overall differences among populations. To control for possible environmental effects, offspring of eight clones from two populations (Belize and Florida) were reared at 25 C and similarly analyzed. All characters with the exception of pectoral fin rays were significantly different among wild populations. In addition, Belizean male fish differed from hermaphrodites in several morphometric characters. Fish reared at constant temperature also displayed significant differences, indicating a probable genetic component to differences in wild fish. The multivariate analyses also confirmed considerable heterogeneity among R. marmorahts. Overall, fish from Brazil, the Florida Everglades, Belize, and Honduras appear to be distinct from the other groups. The characters that contributed most to group delineations were number of precaudal vertebrae, distance from pelvic fin origin to anal fin origin, pectoral fin length, and number of branched caudal rays. Discriminant function analysis was able to classify the fish reared at 25 C to individual clonal heritage, although with a different set of characters than in wild fish.

Long-term retention of self-fertilization in a fish clade

“…The much larger genetic distances between versus within K. marmoratus and K. ocellatus are also obvious in a mitochondrial phylogeny in which individual fish are treated as units of analysis (Fig. 2), and they are consistent with separate-species status for these two taxa (24). A qualitatively similar pattern of relationships is apparent in a microsatellite phenogram of populations (Fig.…”

Deep and concordant subdivisions in the self-fertilizing mangrove killifishes (Kryptolebias) revealed by nuclear and mtDNA markers

“…Our surveys resulted in samples covering most of the geographic distribution of the K. marmoratus species complex, including several geographic areas where these species have not previously been reported. Identification of species in the K. marmoratus complex is difficult using morphological characters (Taylor, 2003), but the three valid species of the complex (K. ocellatus, K. hermaphroditus and K. marmoratus) are easily distinguishable with genetic markers such as microsatellites or mitochondrial DNA (mtDNA) (Tatarenkov et al, 2009(Tatarenkov et al, , 2011. Therefore, instead of trying to fit our collections into a particular species based on morphology, we chose to first determine major genetic groupings of the selfing mangrove rivulus and only then evaluate how these groups agree with current taxonomy.…”

Phenotypic Plasticity and Integration in the Mangrove Rivulus (Kryptolebias marmoratus): A Prospectus

“…Lin and Dunson (1995) showed genotype effects on egg volume and hatchling size, Edenbrow and Croft (2011) revealed genotypic effects on age at maturity and on the total number of eggs laid between 105 and 151 days posthatching, and Grageda et al (2005) described genotypic effects on fecundity and growth rates (0-100 days posthatching). Conclusions about genotypelevel differences in life history, behavior, and physiology seem contingent upon the number and identity of the genotypes compared; for instance, Grageda et al (2005) showed minimal differences in morphological characters between Panamanian and Belizean lineages, contrasting Taylor's (2003) evidence for marked differences in a similar set of characters among populations/genotypes derived from various locations in Florida, Belize, Honduras, Bahamas, and Brazil. We should therefore, expand the number of genotypes used in our studies, and perhaps select many genotypes from each of a number of populations that span the fish's geographic range (e.g., Edenbrow and Croft 2011).…”