Douglas M. McElroy

Sexual selection, reproductive behavior, and speciation in the mbuna species flock of Lake Malawi (Pisces: Cichlidae)

The cichlid species flocks of the African Great Lakes represent the most extreme case of adaptive radiation among vertebrates. Recently, attention has focused on the potential for sexual selection to drive or accelerate speciation in these fishes. Cichlids as a whole are social in nature and display complex behavior, particularly during courtship and spawning; however, the extent to which changes in species recognition cues may account for species diversity among haplochromine lineages has remained speculative. Our investigations have indicated that oral incubating haplochromines show a reduction in diversity and extent of courtship relative to substrate brooding cichlids, and apparently retain aspects of a primitive specific mate recognition system. Laboratory observations of courtship in the Malawian endemicPseudotropheus zebra suggest that organization of the spawning bout is loose, and lacking in any well defined stimulus-response chain. Interspecific comparisons of in situ courtship behavior among male mbuna, lithophilous haplochromines of Lake Malawi, revealed only one potential example of species-specific behavior, and indicated that mate choice occurred prior to the onset of intense courtship. Courtship display by male mbuna does not appear critical to species recognition and may represent an evolutionary relict. Alternatively, male courtship display may have an indirect effect on successful reproduction or may be maintained through pleiotropic effects. The mbuna display no evidence of behavioral innovation and show limited interspecific differentiation in behavioral expression. More generally, there is no evidence at present to suggest that epigamic sexual selection, acting on courtship behavior, has been a major mechanism in the diversification of the haplochromine species flocks.

Coloration in African Cichlids: Diversity and Constraints in Lake Malawi Endemics

Male breeding coloration is an obvious and often diagnostic character for species identification among mbuna, the rock-dwelling haplochromine fishes of Lake Malawi. Colour diversification has figured prominently in most models of cichlid speciation, though considerations of colour diversity have been limited. We describe coloration for common species of mbuna by digital colour acquisition techniques and use these data to characterize coloration of the fauna. The range of colour diversity in the mbuna is great; however, patterns of diversity appear somewhat limited. A number of taxa are similar in coloration, and several areas of available colour space are under-represented relative to random expectations. Colour diversification does not appear to be phylogenetically constrained, at least within species complexes. However, weakly significant associations between coloration and ecological characteristics exist. We discuss our results in terms of potential forces acting to influence mbuna coloration, such as phylogenetic or developmental constraints and natural or sexual selection.

Use of Geometric Morphometrics to Differentiate Gila (Cyprinidae) within the Upper Colorado River Basin

Abstract Video images of 215 adult Gila robusta and 148 endangered Gila cypha were collected from May 1991–October 1992 at eight Colorado River basin localities (seven upper basins and one lower basin). The two species were sympatric at five of these locations; G. robusta was absent at one site, whereas G. cypha was missing at two others. Saggital views of each individual were videotaped and 25 morphological points (15 anatomical landmarks and 10 helping points) identified. Bookstein shape coordinates were calculated from Cartesian coordinates of these landmarks and points, whereas centroid size was used as a measure of body size. Shape differences were evaluated among populations of each species using MANOVA and canonical variates analysis. In G. cypha, variation encompassed three aspects: nuchal hump (most pronounced in Grand Canyon forms), relative head size (larger in Cataract Canyon forms), and caudal peduncle dimensions (shorter with a tapering depth in Cataract Canyon forms but longer and uniformly deeper in those from Desolation Canyon). Nuchal development in G. robusta is slight, hence only head and peduncle dimensions distinguished populations. Those individuals from Cataract Canyon had relatively shorter peduncles that (again) tapered in depth from anterior to posterior, whereas G. robusta from Desolation Canyon possessed peduncles that were much longer and of uniform depth. Specimens from Debeque and Rifle Canyons had proportionally smaller heads. Variation among all 13 populations (i.e., both species together) was evaluated using relative warp analysis, with G. cypha and G. robusta clearly separated at all sympatric locations except those from Desolation and Caratact Canyons. Here, body shapes of the two species converged. Overall, shape variation in both species is clinal. Although results from our geometric morphometric analysis were statistically similar to those based on distances derived from a truss analysis, the geometric approach visually demonstrated phenotypic differences among populations and species and this, in turn, has management implications.

Patterns of Morphological Variation among Endangered Populations of Gila robusta and Gila cypha (Teleostei: Cyprinidae) in the Upper Colorado River Basin

The native fish fauna of the American southwest is in decline as a result of habitat destruction, disruption of natural water flows, and introduction of nonnative species. The status of several members of the cyprinid genus Gila occurring in the upper Colorado River basin is particularly tenuous, in part because of uncertainty regarding their taxonomic status. To examine this uncertainty, we have sampled 363 specimens of G. robusta and G. cypha from eight localities in the upper Colorado River basin and the Grand Canyon and used canonical discriminant and cluster analysis to categorize patterns of morphological variation at three levels of biological organization. At the population level, all sampled populations of both species differed significantly, although there was no relationship between morphological similarity and geographic proximity of populations in either species. At the species level, the two forms were clearly distinct in morphology whether in sympatry or in allopatry. At the generic level, we found two somewhat contradictory results: (1) conspecifics from allopatric localities generally clustered together to the exclusion of heterospecifics; and (2) heterospecific populations at Cataract and Desolation canyons were more similar to one another than to allopatric conspecifics. This locality effect influencing the morphological similarities between species at these sites may be a consequence of either introgressive hybridization and/or convergent local adaptation. In general, allopatric populations of both G. robusta and G. cypha appear to represent independent evolutionary and conservation units. Populations of Gila should not be considered in isolation of congeners or of the environment in which they occur, and biological foresight and an emphasis on habitat conservation should be used in managing these species.

Novel Jaw Morphology in Hybrids between Pseudotropheus zebra and Labeotropheus fuelleborni (Teleostei: Cichlidae) from Lake Malawi, Africa

Interspecific hybridization among haplochromine cichlids of the East African Great Lakes has been proposed as a mechanism for the evolution of new taxa in these highly speciose faunas; however, no obviously hybrid individuals have been collected, nor is it clear whether one could recognize hybrids if they did occur. Here we report on the morphology of experimentally produced F, hybrids between Pseudotropheus zebra and Labeotropheusfuelleborni, two common Lake Malawi rock-dwelling haplochromine taxa (mbuna) that differ substantially in trophic morphology. We qualitatively describe the morphology of hybrids, and quantitatively analyze 13 descriptors of oral morphology using both univariate and multivariate procedures. Hybrids, although morphologically distinct, more closely resemble P. zebra than L.fuelleborni. Three individual oral jaw characters are intermediate in, and thus diagnostic of, hybrids; however, hybrids display unique patterns of expression for five characters. Discriminant function and canonical variates analysis clearly separate all three groups. The position of hybrids along canonical variate II suggests that hybrids are neither intermediate nor mosaic but rather display a novel multivariate phenotype. Our results suggest that (1) interspecific hybridization between these taxa does not occur under current conditions in Lake Malawi, (2) the genetic control of mbuna trophic morphology may involve a significant dominance component, and (3) hybrids (when produced) may lie along an ecomorphological trajectory distinct from that separating parents. As a consequence, we propose that phenotypic shifts in cichlid populations may be discontinuous and involve limited regulatory genetic change and that hybridization (if of historical importance) could result in the production of novel phenotypes with unique evolutionary potentials.

The Upper Green River Barcode of Life Project

Abstract The DNA barcoding initiative is an international effort to collect standardized DNA sequences from each Eukaryotic species to facilitate taxonomy and specimen identification. DNA barcoding experiments, because they are not technically difficult, are well suited to being used as investigative research experiences in a teaching laboratory. We have implemented a DNA barcoding exercise for our first year “Undergraduate Experience” students in which participants catch arthropods from our university field station, the Upper Green River Biological Preserve. The arthropod specimens were brought to the laboratory, mounted, photographed, and identified via keys and field guides based on morphological characters. This identification served as a working hypothesis for the identity of each specimen. A single leg was removed from each specimen, DNA was extracted, and a fragment of the cytochrome oxidase I gene was PCR amplified and sequenced. Then, using bioinformatics tools, the sequence for each specimen was compared to those in the Barcode of Life and Genbank nucleotide databases. A second species diagnosis based on DNA sequence matches was determined, which could be compared to the original morphological identification, serving as a test of that hypothetical species identity. In its first semester of implementation, 28 arthropod barcodes were produced, which will be augmented by the work of future classes.

DISCRIMINATING GILA ROBUSTA AND GILA CYPHA: RISK ASSESSMENT AND THE ENDANGERED SPECIES ACT

Several sympatric Colorado River basin cyprinid fishes of the genus Gila are federally protected, yet difficulty in identifying individuals to species has limited recovery efforts. Using five characters easily scored in the field, we quantified morphological variation in G. robusta and G. cypha from eight localities, comparing discriminatory power of these data to that of a previous multivariate truss analysis of the same specimens. Significant between-species differences existed in four characters; three displayed patterns consistent with typological differences between species. Success of post hoc identification of specimens exceeded 70% for these three characters and increased to >82% by incorporating variables into a discriminant function. Nevertheless, potentially diagnostic features were relatively uncorrelated within individuals, and little congruence existed between different characters. Multivariate analyses clearly discriminated between sympatric species pairs despite considerable variation amon...

Exposure to acute low pH impairs chemoreception and feeding performance in larval fathead minnows (Pimephales promelas)

The impact of acute low pH exposure on feeding performance was investigated in larval fathead minnows. Sets of larvae were subjected to each of three pH concentrations (4.5, 5.5 and 7.7) under various conditions designed to isolate different sensory modalities. Temporal patterns in locomotor activity and number of larvae feeding were analyzed. Levels of locomotor activity were uncorrelated with feeding rates and were qualitatively different early vs. late in the larval phase. Under most conditions, locomotor activity decreased during the first few days posthatching, then increased over the remainder of the study. In contrast, feeding activity increased continually. Mechanoreception appeared to play a significant role in prey capture at pH 7.7, while photoreception contributed little. pH exposure had a significant negative impact on feeding success, though the nature of this effect varied with test conditions. Exposure to pH 4.5 appeared to strongly inhibit chemoreception; data also suggest close coupling ...