When competing for food or other resources, or when confronted with predators, young animals may be at a disadvantage relative to adults because of their smaller size. Additionally, the ongoing differentiation and growth of tissues and the development of sensory-motor integration during early ontogeny may constrain performance. Because ectothermic vertebrates show different growth regimes and energetic requirements when compared to endothermic vertebrates, differences in the ontogenetic trajectories of performance traits in these two groups might be expected. However, both groups of vertebrates show similar patterns of changes in performance with ontogeny. Evidence for compensation, resulting in relatively high levels of performance in juveniles relative to adults, appears common for traits related to locomotor and defensive behaviors. However, there is little evidence for compensation in traits associated with feeding and foraging. We suggest that this difference may be due to different selective regimes operating on locomotor versus feeding traits. As a result, relatively high levels of locomotor performance in juveniles and relatively high levels of feeding performance in adults are observed across a wide range of vertebrate groups.

Resource polymorphisms, or morphological variations related to resource use, are common in fishes and are thought to be a possible step in speciation. This study experimentally tests the hypothesis that fitness (as estimated by growth rates) is increased by the presence of multiple trophic morphotypes (or morphs) within a population. Cage experiments were used to quantify the intraspecific competitive interactions between morphs of the polymorphic cichlid Herichthys minckleyi in Cuatro Ciénegas, Mexico. Results suggest that competition is reduced between morphs in mixed‐morph treatments relative to equal‐density single‐morph treatments. Field studies revealed that the morphs feed in different microhabitats and use different feeding behaviors within these microhabitats. These results suggest that the polymorphism is maintained in the population because it decreases competition between the morphs, and that differences in feeding behavior facilitate resource partitioning. Corresponding Editor: S. Nylin.

Teleost fishes typically first encounter the environment as free-swimming embryos or larvae. Larvae are morphologically distinct from adults, and major anatomical structures are unformed. Thus, larvae undergo a series of dramatic morphological changes until they reach adult morphology (but are reproductively immature) and are considered juveniles. Free-swimming embryos and larvae are able to perform a C-start, an effective escape response that is used evade predators. However, escape response performance improves during early development: as young fish grow, they swim faster (length-specific maximum velocity increases) and perform the escape more rapidly (time to complete the behavior decreases). These improvements cease when fish become juveniles, although absolute swimming velocity (m s(-1)) continues to increase. We use studies of escape behavior and ontogeny in California halibut (Paralichthys californicus), rainbow trout (Oncorhynchus mykiss), and razorback suckers (Xyrauchen texanus) to test the hypothesis that specific morphological changes improve escape performance. We suggest that formation of the caudal fin improves energy transfer to the water and therefore increases thrust production and swimming velocity. In addition, changes to the axial skeleton during the larval period produce increased axial stiffness, which in turn allows the production of a more rapid and effective escape response. Because escape performance improves as adult morphology develops, fish that enter the environment in an advanced stage of development (i.e., those with direct development) should have a greater ability to evade predators than do fish that enter the environment at an early stage of development (i.e., those with indirect development).

SUMMARYMudskippers use pectoral fins for their primary mode of locomotion on land and pectoral fins in conjunction with the axial musculature and caudal fin to move in water. We hypothesized that distinct pectoral fin movements enable effective locomotion in each environment. Additionally, we made three functional predictions about fin movements during locomotion on land versus water: the pectoral fin is depressed more on land than in water; the pectoral fin will have greater changes in fin area between propulsive and recovery phases in water versus land; anterior and posterior excursions will be greater on land than in water. Locomotion was recorded in each environment using a high-speed digital-imaging system and kinematic variables were calculated from digitized landmark points. Variables were analyzed using principal components analysis and matched pairs ttests. Mudskippers produce distinct kinematic patterns across environments (P<0.003), although only some of our predictions were supported. The magnitude of fin depression is the same across habitats. However, depression occurs during the propulsive phase on land (by -0.60 cm), whereas during the propulsive phase in water the fin is elevated (by +0.13 cm). We were unable to support the hypothesis that fin orientation differs between environments. Lastly, anterior extension of the fin is greater on land (1.8 cm, versus 1.3 cm in water), creating a larger stride length in this environment. We posit that the mudskipper pectoral fin may facilitate stability in water and thrust production on land, and suggest that the robust fin morphology of the goby lineage may predispose species within this group to terrestrial locomotion.

Fabrication of electrospun fibrous scaffolds as future medical devices is being widely researched, with particular emphasis given to their material properties and effect on cell response and differentiation. However, the vast majority of these scaffolds are sterilized via nonmedically approved methods, including submersion in ethanol and exposure to UV light. Although these techniques are adequate for laboratory-based research, they are not sufficient for human implantation. In this case, regulatory approved, medical grade sterilization is required. In this study, we report the effects of gamma irradiation, a regulatory approved technique, on electrospun poly(ecaprolactone) fibers. Fabricated fibers were separately subjected to different dosages of irradiation ranging from 0 to 45 kGy and then assessed for their physicochemical properties. Gamma irradiation affected fiber properties irrespective of dosage. A dose-dependent decrease in polymer molecular weight was observed and an increase in melting point and crystallinity reported. Similarly, irradiation had a significant effect on mechanical properties with greatest decrease in tensile strength (68%) for fibers exposed to 40 kGy. The method of sterilization had no effect on cell response. Seeded tenocytes attached to all fibers and elongated parallel to the underlying fiber direction. The results demonstrate the importance of incorporating medical grade sterilization procedures early in the research projects time line to assist translation from bench to clinic.