Cyprinodon Pecosensis Research Articles

Habitat-Morphotype Associations of Pecos Pupfish (Cyprinodon pecosensis) in Isolated Habitat Complexes

Alterations to the Pecos River in New Mexico and Texas, USA, including damming and river channelization, plus water extraction and diversion from, and pollution of associated habitats during the 19th and 20th centuries have greatly impacted many fish species. The Pecos pupfish (Cyprinodon pecosensis) is one species that was heavily impacted, especially because introduction of a congener, the sheepshead minnow (C. variegatus), to the Pecos River in the 1980s eliminated pure C. pecosensis from most of its range via hybridization. Currently, C. pecosensis is restricted to generally small isolated habitats, although historically this species had a large metapopulation with a large geographic range. The current study was an initial survey of morphological variation within different isolated habitat complexes to determine if there were habitat-morphotype distinctions. We used analysis of convex hull coverage (ACHC) with geometric morphometric data to assess whether morphotypes were distinct. ACHC results confir...

The Role of Hybrid Vigor in the Replacement of Pecos Pupfish by Its Hybrids with Sheepshead Minnow

Abstract: Many species are jeopardized by hybridization and genetic introgression with closely related species. Unfortunately, the mechanisms that promote or retard gene flow between divergent populations are little studied and poorly understood. Like many imperiled fish species, the Pecos pupfish (Cyprinodon pecosensis) is threatened with replacement by its hybrids with a close congener. We examined swimming performance and growth rate of hybrid pupfish to determine the role of hybrid vigor in the genetic homogenization ofC. pecosensisby its hybrids with sheepshead minnow (C. variegatus). The F1 hybrids, backcross hybrids, and purebredC. variegatusdisplayed greater swimming endurance than purebredC. pecosensis. In addition, F1 hybrids andC. variegatusgrew more rapidly thanC. pecosensis. The ecological superiority of hybrids probably promoted their rapid spread through and beyond the historic range ofC. pecosensis. These results indicate that eradication of hybrids and restoration ofC. pecosensisto its native range is unlikely. Extinction of unique speciesviagenetic homogenization can result from human activities that increase gene flow between historically fragmented populations; conservation managers must weigh the potential for such a catastrophe against the presumed benefits of increased interpopulation gene flow. This example illustrates how, after hybridization has occurred, conflict may arise between formerly complementary conservation goals.

Populations of Pecos pupfish ( Cyprinodon pecosensis ) differ in their susceptibility to hybridization with sheepshead minnow ( C. variegatus )

The importance of sexual selection in hybridization between species that evolved in allopatry is poorly understood. Even less is known about differences between populations in their resistance or susceptibility to genetic introgression with a congener. Here we examine behavioral differences between populations of the native Pecos pupfish (Cyprinodon pecosensis) and their potential effects in facilitating or retarding hybridization with an introduced congener, the sheepshead minnow (C. variegatus). We quantified competitive interactions, establishment of territories, and mating success of several naturally occurring C. pecosensis populations and an artificially created laboratory population (control) against C. variegatus. Experiments were conducted in large outdoor tanks during the summer months when high temperatures favor breeding activity in pupfish. C. pecosensis populations differed in agonistic behavior, territoriality, and in mating success when competing against C. variegatus. Differences in the competitive ability of males from different C. pecosensis populations suggest that the rate of introgression with C. variegatus may vary, depending on the population of C. pecosensis it comes in contact with. Our results suggest that large, stable C. pecosensis populations may be relatively resistant to hybridization with C. variegatus. Interpopulation variation in male behavior, shaped by sexual selection, may be important in determining the incidence and rate of hybridization between the two congeners. Experimental studies are a powerful tool in elucidating behavioral processes, such as the action of intrasexual selection, that facilitate or retard the coalescence of lineages through initial hybridization and subsequent genetic introgression after secondary contact between allopatric species.

Sexual selection promotes hybridization between Pecos pupfish, Cyprinodon pecosensis and sheepshead minnow, C. variegatus.

Rapid and extensive genetic introgression has occurred between Pecos pupfish (Cyprinodon pecosensis) and sheepshead minnow (Cyprinodon variegatus) in the wild. We studied both female mate choice and male-male competition for mates among C. pecosensis, C. variegatus, and their F1 hybrids to determine what role these behaviours played in the formation of the hybrid swarm. Female C. pecosensis preferred male C. variegatus to conspecific males, C. variegatus females displayed no significant preference when given a choice between purebred males, and neither C. pecosensis nor C. variegatus females discriminated against F1 hybrid males. We found no evidence for female olfactory recognition of mates. Male F1 hybrids and C. variegatus were more aggressive than C. pecosensis males, achieving greater reproductive success under two different experimentally-induced mating systems. Hybrids were superior to C. variegatus when only two males competed (dominance interactions), but the two types were competitively equivalent in a territorial mating system. Our results indicate that active inter- and intra-sexual selection contributed to the accelerated hybridization between these two species. By including the possibility that some aspects of a hybridization and introgression event may be under positive selection, researchers may better understand the dynamics that lead to hybrid zone stability or the spread of introgressed genetic material.

Threatened Fishes of the World: Cyprinodon pecosensis Echelle & Echelle, 1978 (Cyprinodontidae)

Common name: Pecos pupfish. Conservation status: Threatened status in Texas and New Mexico. Identification: Only scales on the abdomen are in a patch anterior to the pelvic fins and one posterior to the gill membrane isthmus (Echelle & Echelle 1978). Males have larger dorsal and anal fins, a dark bar on the distal portion of the caudal fin and an iridescent blue nape (Echelle & Echelle 1978). Females are cryptically colored olive-brown and the dorsal fin is marked by a dark ocellus. Juveniles of both sexes have the female color pattern. Contrary to the typical pupfish pattern, young males may lose the dorsal ocellus before onset of sexual maturity; however, in the presence of large, mature males, young adult males may retain the female color pattern (Garrett 1981a) as well as behavior (Kodric-Brown 1977). Drawings by Robert G. Howells. Distribution: Originally occurring in the Pecos River system from Roswell, New Mexico to Independence Creek, Terrell County, Texas, its range is now restricted to just a few locations (Propst 1999).

Sexual selection, stabilizing selection and fluctuating asymmetry in two populations of pupfish (Cyprinodon pecosensis)

Fluctuating asymmetry of morphological traits is thought to reflect the capacity of a genotype to produce an integrated, functional phenotype. I tested three predictions. (1) In a polygynous breeding system, under intense sexual selection on males, breeding males should show greater symmetry in bilaterally symmetrical traits than non-breeding males or females. (2) If these traits are under stabilizing selection, highly symmetrical individuals also should be modal phenotypes, thus near the mean value for that trait, whereas individuals with increased asymmetry should represent marginal phenotypes, near the extremes of the distribution for that trait. (3) Differences in the intensity of sexual selection should be reflected in differences in the degree of fluctuating asymmetry between sexes among populations. I examined the relationship between male breeding status and the degree of fluctuating asymmetry of four bilaterally symmetrical traits, preorbital and preopercular pores and pectoral and pelvic fin rays, in two populations of Pecos pupfish which differed in the intensity of sexual selection. These traits do not function in male-male competition or female choice, thus are not directly affected by sexual selection. In Mirror Lake breeding males, as a group, were most symmetrical for all four traits, while non-breeding males and females showed higher levels of fluctuating asymmetry. Similarly, symmetrical individuals also represented modal phenotypes for four traits (breeding males), and for three traits (non-breeding males and females). These patterns were not seen in the Lake Francis population, where breeding males were as asymmetrical as non-breeding males and females, and the degree of fluctuating symmetry did not differ between modal and marginal phenotypes for any of the four traits. When ecological conditions favour intense sexual selection, either through female choice, male-male competition, or both, breeding males represent the most fit phenotypes. Thus sexual selection reinforces the effects of stabilizing selection on characters that do not function as secondary sexual traits. However, when sexual selection is relaxed, differences between sexes disappear.

Sexual selection, stabilizing selection and fluctuating asymmetry in two populations of pupfish (Cyprinodon pecosensis)

Fluctuating asymmetry of morphological traits is thought to reflect the capacity of a genotype to produce an integrated, functional phenotype. I tested three predictions. (1) In a polygynous breeding system, under intense sexual selection on males, breeding males should show greater symmetry in bilaterally symmetrical traits than non-breeding males or females. (2) If these traits are under stabilizing selection, highly symmetrical individuals also should be modal phenotypes, thus near the mean value for that trait, whereas individuals with increased asymmetry should represent marginal phenotypes, near the extremes of the distribution for that trait. (3) Differences in the intensity of sexual selection should be reflected in differences in the degree of fluctuating asymmetry between sexes among populations. I examined the relationship between male breeding status and the degree of fluctuating asymmetry of four bilaterally symmetrical- traits, preorbital and preopercular pores and pectoral and pelvic fin rays, in two populations of Pecos pupfish which differed in the intensity of sexual selection. These traits do not function in male-male competition or female choice, thus are not directly affected by sexual selection. In Mirror Lake breeding males, as a group, were most symmetrical for all four traits, while non-breeding males and females showed higher levels of fluctuating asymmetry. Similarly, symmetrical individuals also represented modal phenotypes for four traits (breeding males), and for three traits (non-breeding males and females). These patterns were not seen in the Lake Francis population, where breeding males were as asymmetrical as non-breeding males and females, and the degree of fluctuating symmetry did not differ between modal and marginal phenotypes for any of the four traits. When ecological conditions favour intense sexual selection, either through female choice, male-male competition, or both, breeding males represent the most fit phenotypes. Thus sexual selection reinforces the effects of stabilizing selection on characters that do not function as secondary sexual traits. However, when sexual selection is relaxed, differences between sexes disappear.

Morphological variation in intergrade pupfish populations from the Pecos River, Texas, U.S.A.

In the early 1980s, sheepshead minnow Cyprinodon variegates was introduced into the Pecos River, Texas, U.S.A. where it hybridized with the endemic Pecos pupfish C. pecosensis. By 1985, pupfish populations throughout approximately 300 km of the river consisted exclusively of individuals of hybrid origin (intergrades). There was significant (P <0·05) geographic variation in most morphological characters; the general pattern of variation was of a bidirectional cline centred near Pecos, Texas. At that site, morphology of intergrade populations resembled mostly that of the introduced species. Upstream and downstream from Pecos, morphology shifted progressively toward that typical of the native form. Intergrade populations were morphologically intermediate to the parental forms, showed a rapid approach to random assortment of characters, and generally exhibited greater morphological variability than occurred in either parent species. These observations and the consistent lack of bimodality in frequency distributions of a morphological hybrid index support the contention that intergrade populations comprise panmictic admixtures of C. variegates and C. pecosensis.

DEVELOPMENT OF THE HYBRID SWARM BETWEEN PECOS PUPFISH (CYPRINODONTIDAE: CYPRINODON PECOSENSIS) AND SHEEPSHEAD MINNOW (CYPRINODON VARIEGATUS): A PERSPECTIVE FROM ALLOZYMES AND mtDNA.

A comparison of allozyme and mtDNA frequencies was used for insight into a situation in the Pecos River, Texas where contact between the endemic pupfish (Cyprinodon pecosensis) and an introduced congener (C. variegatus) has resulted in rapid, geographically extensive genetic introgression. Temporal changes in mean frequencies of diagnostic allozyme markers indicate that the clinal pattern of introduced genetic material (Echelle and Connor 1989) is slowly decreasing in amplitude. Significant rank concordance in diagnostic allele frequencies among sites and across sampling years indicates directional influences upon temporal allele frequency change. These observations are consistent with the theory of gene flow in neutral clines. Levels of introgression indicated by each of four allozyme loci and mtDNA were roughly equivalent. The early history of the hybrid swarm is explained by genetic swamping, possibly mediated by selection for C. variegatus or C. variegatus × C. pecosensis, at a time when the normally abundant endemic species had been catastrophically depleted. High frequencies of an introduced GPI-A allele in all samples of intergrades suggests that the introduced genome originated with a single founding event.

Role of male-male competition and female choice in the development of breeding coloration in pupfish (Cyprinodon pecosensis)

The function of male breeding coloration and the conditions under which it is expressed were investigated using two experimental protocols that differed in the degree of control of social factors. In tank experiments, focal males were separated by opaque or clear partitions or allowed to interact freely without partitions. In lake experiments, males were introduced into opaque or clear enclosures in the lake from which they were collected. This design tested the relative importance of breeding substrate, social interactions with other males, and presence of females and juveniles on the expression of breeding coloration and agonistic and mating behavior in pupfish. Breeding coloration was not expressed in the absence of conspecifics, even in the presence of suitable breeding substrate, or in the presence of juveniles. Breeding coloration was poorly developed when only males were present, was more intense in the presence of females, and darkened significantly after a spawning bout Males in clear enclosures in their natural lake habitat were in visual contact with conspecifics of both sexes and developed more intense blue breeding coloration than males in the tank experiments that were in visual contact only with other males. Uncon-fined males with territories in the lake developed the most intense breeding coloration. Breeding coloration of male pupfish is a facultative trait that is well developed when breeding females are present and plays a major role in the attraction and courtship of mates. However, maximum development of breeding coloration by territorial males suggests that intrasexual and intersexual selection act concordantly on this trait.[Behav Ecol 7: 431-437 (1996)]

Does part reproductive history predict competitive interactions and male mating success in pupfish?

Two experiments were performed to determine the effect of past territoriality and mating success on subsequent dominance and ability to attract females. First, in 14 staged, pair-wise encounters, the development of nuptial coloration and agonistic behaviour was examined in two types of males: previously territorial (PT) and previously non-territorial (PNT) males. Previously territorial males developed a more intense nuptial coloration and won all contests. Second, to test the males' ability to attract females, other factors were controlled that could have affected female mate choice, such as male size, quality of breeding substrate and male-male interactions. In 40 trials, PT males were more active, developed a more intense nuptial coloration, courted females more vigorously, spawned sooner and had a higher mating success than PNT males. Thus, in pupfish, Cyprinodon pecosensis, previous reproductive history is a good indicator of both dominance and mating success. Only males in good physical condition achieve high mating success, and both intra- and inter-sexual selection are important in maintaining the close correlation between expression of nuptial coloration, a second sexual trait, and other male attributes, such as physical condition and vigour, that allow a male to secure and defend a territory against rivals and to attract and spawn with females.

The relationship between physical condition and social status in pupfish Cyprinodon pecosensis

The relationship between physical condition and social status in pupfish Cyprinodon pecosensis

The breeding system of pupfish, Cyprinodon pecosensis: effects of density and interspecific interactions with the killifish, Fundulus zebrinus

The relative importance of intraspecific competition and interspecific competition with killifish on the breeding activities of territorial male pupfish was investigated in two populations. Compared to Lake Francis, pupfish densities in Mirror Lake were higher, individuals were larger, and intraspecific aggression was more important than interspecific interactions with killifish. Killifish had little impact on the activity budgets of territorial male pupfish, but were excluded from favored breeding habitats. The opposite pattern was observed in Lake Francis. Killifish were numerically dominant as well as relatively larger than pupfish, and they interfered with the breeding activities of territorial males. In Lake Francis most of the agonistic activities of territorial male pupfish were directed toward killifish. Asymmetries in the interactions between pupfish and killifish in the two lakes also were reflected in qualitative and quantitative differences in the breeding activities of pupfish. In Mirror Lake the frequency of agonistic and breeding behaviors increased over the breeding season, but in Lake Francis they decreased. The underlying factors responsible for the observed competitive asymmetries between the species in the two habitats are not known. However, the higher salinity tolerances of pupfish may, in part, have accounted for both their numerical dominance and their size-advantage over killifish in the more saline environment of Mirror Lake. Physiological and ecological factors may thus play an important role in the outcome of competitive asymmetrics between species.

Genetic Status of Pecos Pupfish Populations after Establishment of a Hybrid Swarm Involving an Introduced Congener

Abstract We used protein electrophoresis to study the distribution of hybrids between Pecos pupfish Cyprinodon pecosensis and introduced sheepshead minnow C. variegatus in the Pecos River, New Mexico–Texas. Pecos pupfish populations in New Mexico apparently are free of hybrid influence except in waters near the New Mexico–Texas state boundary. In Texas, hybrids have replaced Pecos pupfish throughout 430 km of the Pecos River and have spread into downstream areas well outside the recorded range of Pecos pupfish. Hybrids are nearly ubiquitous in waters peripheral to the river, occurring in irrigation canals, reservoirs, and water-filled, commercial gravel pits. Unintrogressed Texas populations of Pecos pupfish occur only in a small tributary of the Pecos River and in a large gravel pit. Similarities in the genetic structure of hybrid pupfish populations in the Pecos River and peripheral waters suggest that the spread of alleles characteristic of sheepshead minnow has been accomplished by dispersal of hybrid...

Sexual selection is stabilizing selection in pupfish (Cyprinodon pecosensis)

One of the predictions of the ‘good genes’ model of sexual selection is that reproductively successful males with well-developed indicator traits should show smaller variances for non-indicator traits, that are not directly associated with mating success, when compared to non-breeding males and females. Thus sexual selection should reinforce stabilizing natural selection in reducing the variance in quantitative traits. This prediction is tested by analysing variation in eight morphological traits of breeding males, non-breeding males, and females of pupfish (Cyprinodon pecosensis). Breeding males tended to be less variable than non-breeding males for all principal component factors, and for all morphological traits except for depth, although these differences were statistically significant only for PC2, and PC5 and for pelvic fin length, number of pelvic fin rays and number of preopercular and preorbital pores. Similarly, breeding males tended to be less variable than females for all principal component factors and for all morphological traits except for number of preopercular pores. These differences were statistically significant for PC2, and for depth, pelvic fin length, number of preorbital pores and pectoral fin rays. The overall pattern of reduced variability in independent traits of breeding males revealed by principal component analysis is very consistent and highly significant (P<105). These results support the prediction of the ‘good genes’ model and show that reproductively active males are subject to more severe stabilizing selection for several quantitative traits than non-breeding males and females. Thus sexual selection, through male-male competition, female choice, or an interaction of both selective processes, results in stabilizing selection on quantitative morphological traits.

Effects of sex-ratio manipulation on territoriality and spawning success of male pupfish, Cyprinodon pecosensis

The sex ratio of Cyprinodon pecosensis was manipulated by varying the number of females but not of males. This resulted in some subordinate males changing their breeding tactics from satellites to territorials. The spawning success of breeding males was directly related, and the intensity of male-male competition was inversely related, to the number of available females. Time-budget data indicated a tradeoff between courtship and agonistic behaviour. In the male-biased treatment, males engaged in a greater number of agonistic interactions and fewer courtship bouts; conversely, in the female-biased treatment courtship behaviour was more frequent than aggression. A greater proportion of males adopted the satellite breeding tactic in the male-biased and even-sex-ratio treatments. Smaller, competitively inferior males were most sensitive to changes in the sex ratio. In the female-biased treatment, with an increase in mating opportunities and a decrease in the level of male-male competition for females, average mating success increased, more males were able to defend territories, and some satellite individuals were able to adopt the territorial breeding tactic. Temporal or spatial changes in the operational sex ratio of a population may have profound effects on the dynamics of the breeding system by affecting (1) the proportion of males adopting primary and secondary breeding tactics, (2) variance in reproductive success, and (3) intensity of sexual selection.

Effect of Population Density, Size of Habitat and Oviposition Substrate on the Breeding System of Pupfish (Cyprinodon pecosensis)

AbstractSize of habitat, availability of oviposition substrate, and population density were manipulated to determine their effects on the structure and dynamics of the pupfish breeding system. The fish established a territorial breeding system in large tanks, irrespective of population density or oviposition substrate. A dominance hierarchy, in which one male controlled most of the oviposition substrate and spawned with most females, was established in small tanks at low densities. Both population density and oviposition substrate affected the number of males defending territories. Male spawning success was inversely related to availability of oviposition substrate, but was not affected either by density or tank size. Location of a territory and its size also influenced spawning success. Males with bigger territories had higher spawning success. A “carryover” effect of neighbors was observed; males with reproductively active neighbors spawned more often than those with less successful neighbors. Interference with spawning was affected both by tank size and density. Agonistic behavior of breeding males was not affected by any manipulation, but it was positively associated with male spawning success at high but not at low densities. In all treatments the mortality of breeding males was approximately 8 times as high as that of females, suggesting that, under these experimental conditions, the cost of reproducing is substantially higher for males. Comparisons between breeding pupfish in these experiments and in natural environments provide a basis for understanding the selective pressures that have favored the maintenance of these extremely plastic breeding systems.

Satellites and sneakers: opportunistic male breeding tactics in pupfish (Cyprinodon pecosensis)

Manipulations of population density, availability of oviposition substrate, and size of breeding habitat affected the proportion of pupfish (Cyprinodon pecosensis) males adopting territorial and satellite breeding tactics. Satellites occupied stations above breeding substrates defended by territorial males. Both territorial and satellite males developed a bright blue breeding coloration. A third breeding tactic, sneak-spawning, was occasionally observed. Sneak-spawning males retained the cryptic female coloration and occasionally spawned on territories. The lower reproductive success of satellites and sneak-spawning males suggested that both are conditional breeding tactics adopted by competitively inferior males. Satellites were present in all treatments that favored a territorial breeding system, but were absent when the breeding system was a dominance hierarchy. Satellites were associated with territorial males that had higher reproductive success and larger territories than males without satellites. Satellites functioned as parasites rather than as mutualists, since they disrupted spawnings and stole copulations from territorial males. The occurrence and frequency of the conditional breeding behaviours in pupfish represent facultative responses of males to changes in the intensity of competition for breeding sites and females.

Determinants of male reproductive success in pupfish ( Cyprinodon pecosensis)

Studies of the territorial breeding system of Cyprinodon pecosensis at Bottomless Lakes State Park, New Mexico revealed that male reproductive mating success was affected by (a) the topographic features of a territory, and (b) the intensity of male breeding coloration. The importance of male nuptial coloration was demonstrated by increased male reproductive success with intensity of colour of the same individual males (‘light’, 1.6 females mated per h; ‘dark’, 5.4 females mated per h). A stepwise multiple regression analysis of male reproductive success as a function of breeding substrate, nuptial colour, size and agonistic behaviour indicated that topographic complexity accounted for as much as 65.4% of the variance in male reproductive success and coloration accounted for at least an additional 12.7% of the variance. Male size and agonistic behaviour together explained only an additional 1.8% of the variance in reproductive success, and thus were fairly unimportant as indicators of female choice. A high correlation between nuptial colour and reproductive success indicates that females choose males independent of the quality of their territories.

Variation in the Reproductive Traits of the Pecos Pupfish, Cyprinodon pecosensis

The reproductive traits of two populations of Cyprinodon pecosensis were studied and both populations were found to vary several reproductive components. This was demonstrated in nature and in experimental manipulations by changes in each of the measured parameters. Both seem to have similar potential in ovary and clutch size. Egg size, however, appears to have a genetically fixed range that is different for each population. Two populations of Cyprinodon pecosensis from the Bitter Lake National Wildlife Refuge, Chaves Co., New Mexico, were studied. The southern end of the refuge con- tains a series of artificial impoundments (Units 3, 5, 6, 7, 15 and 16) designed to ac- commodate migratory waterfowl. The units are very shallow, averaging less than lm in depth with bottoms composed of flocculent organic detritus. The northern part of the refuge is closed to the public and contains more than 30 gypsum sinkholes of various sizes and with varied biotic assemblages. Study populations were chosen from two extremely different habitats, a large ephemeral impoundment (Unit 16) and a small, relatively stable sinkhole (Hole 10). The habitat differences are perhaps best exemplified by the variations in their water levels. The surface area of Unit 16 can vary annually from a maximum of 80 ha to a