Eric J. Billman

Ontogeny and sex alter the effect of predation on body shape in a livebearing fish: sexual dimorphism, parallelism, and costs of reproduction

Predation can cause morphological divergence among populations, while ontogeny and sex often determine much of morphological diversity among individuals. We used geometric morphometrics to characterize body shape in the livebearing fish Brachyrhaphis rhabdophora to test for interactions between these three major shape-determining factors. We assessed shape variation between juveniles and adults of both sexes, and among adults for populations from high- and low-predation areas. Shape differed significantly between predation regimes for all juveniles regardless of sex. As males grew and matured into adults, ontogenetic shape trajectories were parallel, thus maintaining shape differences in adult males between predation environments. However, shape of adult females between predation environments followed a different pattern. As females grew and matured, ontogenetic shape trajectories converged so that shape differences were less pronounced between mature females in predator and nonpredator environments. Convergence in female body shape may indicate a trade-off between optimal shape for predator evasion versus shape required for the livebearing mode of reproduction.

Comparison of the Efficacy of Iodine, Formalin, Salt, and Hydrogen Peroxide for Control of External Bacteria on Rainbow Trout Eggs

Abstract Two experiments were conducted in vivo with eggs of rainbow trout Oncorhynchus mykiss to compare the bactericidal ability of four common disinfectants. A third test compared bacterial abundance estimation methods for fish eggs (use of a vortex mixer for agitating an egg versus rolling the egg across a petri dish). In the first test, the number of colony forming units (CFU) counted on enriched Ordahls agar with tobramycin (EOT) or trypticase soy agar (TSA) was compared among eggs treated with various doses of iodine, hydrogen peroxide, formalin, or rock salt. A treatment of 1,667 mg of formalin/L of water and all iodine, salt, and hydrogen peroxide treatments had significantly fewer bacteria on EOT than did controls, but CFU counts for a formalin treatment of 500 or 1,000 mg/L did not. All chemical treatments significantly reduced CFU counts on TSA relative to controls except salt at 0.030 mg/L and formalin at 500 mg/L. The least growth was observed on iodine-treated eggs. In the second experimen...

Morphological divergence driven by predation environment within and between species of Brachyrhaphis fishes.

Natural selection often results in profound differences in body shape among populations from divergent selective environments. Predation is a well-studied driver of divergence, with predators having a strong effect on the evolution of prey body shape, especially for traits related to escape behavior. Comparative studies, both at the population level and between species, show that the presence or absence of predators can alter prey morphology. Although this pattern is well documented in various species or population pairs, few studies have tested for similar patterns of body shape evolution at multiple stages of divergence within a taxonomic group. Here, we examine morphological divergence associated with predation environment in the livebearing fish genus Brachyrhaphis. We compare differences in body shape between populations of B. rhabdophora from different predation environments to differences in body shape between B. roseni and B. terrabensis (sister species) from predator and predator free habitats, respectively. We found that in each lineage, shape differed between predation environments, consistent with the hypothesis that locomotor function is optimized for either steady swimming (predator free) or escape behavior (predator). Although differences in body shape were greatest between B. roseni and B. terrabensis, we found that much of the total morphological diversification between these species had already been achieved within B. rhabdophora (29% in females and 47% in males). Interestingly, at both levels of divergence we found that early in ontogenetic development, females differed in shape between predation environments; however, as females matured, their body shapes converged on a similar phenotype, likely due to the constraints of pregnancy. Finally, we found that body shape varies with body size in a similar way, regardless of predation environment, in each lineage. Our findings are important because they provide evidence that the same source of selection can drive similar phenotypic divergence independently at multiple divergence levels.

Multiple predators indirectly alter community assembly across ecological boundaries

Models of habitat selection often assume that organisms choose habitats based on their intrinsic quality, regardless of the position of these habitats relative to low-quality habitats in the landscape. We created a habitat matrix in which high-quality (predator-free) aquatic habitat patches were positioned adjacent to (predator-associated) or isolated from (control) patches with single or two species of caged predators. After 16 days of colonization, larval insect abundance was reduced by 50% on average in both the predator and predator-associated treatments relative to isolated controls. Effects were largely similar among predator treatments despite variation in number of predator species, predator biomass, and whether predators were native or nonnative. Importantly, the strength of effects did not depend on whether predators were physically present. These results demonstrate that predator cues can cascade with equal strength across ecological boundaries, indirectly altering community assembly via habitat selection in intrinsically high-quality habitats.

Habitat enhancement and native fish conservation: can enhancement of channel complexity promote the coexistence of native and introduced fishes?

Native fishes worldwide have declined as a consequence of habitat loss and degradation and introduction of non-native species. In response to these declines, river restoration projects have been initiated to enhance habitat and remove introduced fishes; however, non-native fish removal is not always logistically feasible or socially acceptable. Consequently, managers often seek to enhance degraded habitat in such a way that native fishes can coexist with introduced species. We quantified dynamics of fish communities to three newly constructed side channels in the Provo River, Utah, USA, to determine if and how they promoted coexistence between native fishes (nine species) and non-native brown trout (Salmo trutta L.). Native and introduced fishes responded differently in each side channel as a function of the unique characteristics and histories of side channels. Beaver activity in two of the three side channels caused habitat differentiation or channel isolation that facilitated the establishment of native species. The third side channel had greater connectivity to and similar habitat as the main channel of the Provo River, resulting in a similar fish community to main channel habitats (i.e. dominated by brown trout with only a few native fish species). These results demonstrate the importance of understanding habitat preferences for each species in a community to guide habitat enhancement projects and the need to create refuge habitats for native fishes.

Phylogenetic divergence in a desert fish: differentiation of speckled dace within the Bonneville, Lahontan, and upper Snake river basins

ABSTRACT. Historical events have had a great impact on the biogeography of fishes of western North America. We examined the genetic variation of the speckled dace (Rhinichthys osculus) to determine the effects on this species of extensive hydrological changes during the last 10 million years in the Bonneville and Lahontan basins of the Great Basin and the upper Snake River Basin. Eight hundred sixty-nine base pairs of the mitochondrial gene cytochrome b were sequenced from 97 individuals representing 22 populations within these 3 basins, as well as from 2 individuals of longnose dace (Rhinichthys cataractae) that served as outgroups. Additionally, 13 speckled dace sequences representing 3 Bonneville populations were used from GenBank. Phylogenetic relationships were reconstructed using maximum parsimony and maximum likelihood criteria. Analysis of molecular variance was used to determine population structure and to estimate the amount of gene flow across the community boundaries. Three distinct clades were reconstructed representing the Lahontan Basin, the northern Bonneville and upper Snake River basins, and the southern Bonneville Basin. Additionally, most of the population structuring was explained by variation among basins (65.33%) Speckled dace demonstrated high genetic variation. As hypothesized, the northern and southern Bonneville specimens formed separate clades; however, the southern Bonneville clade was basal to a sister clade formed by the northern Bonneville/upper Snake River and Lahontan clades. These relationships indicate that Pliocene connections between the Snake, Lahontan, and Bonneville drainages, rather than more recent Pleistocene connections, best explain population structuring in speckled dace.

Growth and Survival of Juvenile June Suckers in Enclosures in Utah Lake: Feasibility of Modified Cage Culture for an Endangered Species

Abstract An objective of the recovery program for the federally endangered June sucker Chasmistes liorus is to produce large numbers of artificially propagated individuals to augment the wild population and offset recruitment deficits. We tested the feasibility of modified cage culture in Utah Lake, Utah, as a cost-effective addition to the current hatchery program. Specifically, we examined the survival and growth of age-0 June suckers from July to September at two densities (62 and 187 fish/m3) in two cage types (fixed and floating; n = 12 cages total) in a complete factorial design and compared the cost of production with hatchery costs of production. June suckers were not given supplemental feed during the study but instead preyed on zooplankton that drifted into the cages. Mean survival of June suckers was 45.5% and was not significantly different between cage types or density. Cage design significantly affected growth of June suckers, with fish growing larger in floating cages (mean standard length ...

Optimal Temperatures for Growth and Upper Thermal Tolerance of Juvenile Northern Leatherside Chub

Abstract We examined optimal temperatures for growth and the upper thermal tolerance of juvenile northern leatherside chub (Lepidomeda copei). We conducted 2 experiments using the acclimated chronic-exposure method to estimate optimal temperature for growth of age-0 northern leatherside chub (range 12.8–28.3 °C). Upper thermal tolerance was estimated using the critical thermal maximum (CTM) and upper incipient lethal temperature (UILT) methods for fish acclimated at 15, 18, 23, and 28 °C. We also measured stream temperatures in Yellow Creek, Summit County, Utah, during July–August 2006 to compare our results to actual summer stream temperatures. Survival in growth tests was not significantly different between treatment temperatures in either experiment (P > 0.098). The optimal temperature for growth in the 1st trial estimated from the 2nd-order polynomial regression was 23.0 °C, falling outside the range of experimental temperatures (12.8–22.2 °C). The estimated optimal temperature for growth in the 2nd trial was 23.2 °C. In the upper thermal tolerance tests, juvenile northern leatherside chub had CTM values between 29.6 and 35.0 °C; CTM values increased as acclimation temperature increased. Upper incipient lethal temperatures (LT50) ranged from 26.5 to 30.2 °C, increasing with acclimation temperature. Summer stream temperatures in Yellow Creek had a lower mean (14.0–18.1 °C) than did the optimal temperature for growth determined in these studies, but these temperatures exhibited diel fluctuations as large as 15.7 °C.

Effect of age-based and environment-based cues on reproductive investment in Gambusia affinis

We examined the multivariate life-history trajectories of age 0 and age 1 female Gambusia affinis to determine relative effects of age-based and environment-based cues on reproductive investment. Age 0 females decreased reproductive investment prior to the onset of fall and winter months, while age 1 females increased reproductive investment as the summer progressed. The reproductive restraint and terminal investment patterns exhibited by age 0 and age 1 females, respectively, were consistent with the predictions from the cost of reproduction hypothesis. Age 0 females responded to environment-based cues, decreasing reproductive investment to increase the probability of overwinter survival and subsequent reproductive opportunities in the following summer. Age 1 females responded to age-based cues, or the proximity of death, increasing investment to current reproduction as future reproductive opportunities decreased late in life. Thus, individuals use multiple cues to determine the level of reproductive investment, and the response to each cue is dependent on the age of an individual.

A COMPARISON OF MOSQUITO CONSUMPTION AND PREY SELECTION BETWEEN LEAST CHUB (. IOTICHTHYS PHLEGETHONTIS) AND WESTERN MOSQUITOFISH {GAMBUSIA AFFINIS)

Abstract We compared mosquito consumption and prey selection between least chub (Iotichthys phlegethontis) and western mosquitofish (Gambusia affinis) to determine the potential of least chub as an indigenous replacement for mosquito control in Utah. Mosquito consumption was compared between the 2 species in 2 experiments. The first tested consumption at 3 ratios of pupae and larvae (Culex sp.; 1:3, 3:4, and 1:1), and the second tested consumption at varying densities of larvae (967 larvae ·m−3, 1354 larvae ·m−3, and 2258 larvae ·m−3 [30, 42, and 70 larvae per 31-L tank, respectively]). Western mosquitofish consumed more mosquitoes at lower pupae-to-larvae ratios than least chub, but least chub consumed more mosquitoes as the ratio of pupae to larvae increased. Western mosquitofish consumed significantly more larvae than least chub at all densities. Prey selection was compared between least chub and western mosquitofish, either individually or in intraspecific pairs, when the fish were fed equal abundances of 3 prey items: mosquito larvae, Daphnia magna, and midge larvae (Chironomid sp.). Least chub consumed significantly fewer total prey items for both the 1- and 2-fish trials; western mosquitofish consumed significantly more individuals of each prey type except for Daphnia magna in the 1-fish trials. Least chub and western mosquitofish demonstrated no selection for prey items, indicating that both fish would consume mosquito larvae at rates relative to abundance. Feeding habits demonstrated in this study indicated that least chub could be a potential replacement for western mosquitofish for mosquito control; however, field studies should be conducted to assess the ability of both species to control mosquitoes in a natural setting.