Michael H. Horn

Partial α-amylase gene sequences were determined and α-amylase gene expression was quantified in four species of carnivorous, omnivorous, and herbivorous prickleback fishes (family Stichaeidae) to assess the effects of ontogeny, diet, and species on expression of this gene. Pairwise comparison of α-amylase nucleotide sequences revealed 96–98 % identity, and comparison of amino acid portions revealed 93–95 % similarity among the four prickleback species. Expression was determined using in situ hybridization and intensity of expression quantified using image analysis. Alpha-amylase expression level was compared in three feeding categories of the four species: (1) small, wild-caught carnivorous juveniles; (2) larger, wild-caught juveniles of the carnivorous species and the three that had shifted to herbivory or omnivory; and (3) larger, juveniles produced by feeding a low-starch artificial diet to small juveniles until they reached the size of the larger wild-caught juveniles. The results showed no dietary effect in any species but significant ontogenetic and species-level effects in Cebidichthys violaceus, as well as in the sister species Xiphister mucosus and X. atropurpureus. Based on a phylogeny for the Stichaeidae produced for this study using two mtDNA genes and one nuclear gene, the ontogenetic dietary shifts to herbivory/omnivory evolved independently in C. violaceus and in the clade containing the two species of Xiphister. All three of these species increased α-amylase gene expression with increase in size and had higher expression than Anoplarchus purpurescens, which is a member of a third, stichaeid clade comprising carnivores. These results show the importance of α-amylase in the herbivores and omnivores.

Three digestive enzymes in four species of closely related prickleback fishes (family Stichaeidae: Cebidichthys violaceus, Xiphister mucosus, Xiphister atropurpureus and Anoplarchus purpurescens) were analysed to assess whether diet or phylogeny played a larger role in influencing digestive enzyme activity. Cebidichthys violaceus and X. mucosus are primarily herbivorous, whereas X. atropurpureus and A. purpurescens are mainly carnivorous. The two Xiphister species are sister taxa, and A. purpurescens is in a clade adjacent to that of the three other species. Pepsin and trypsin specific activities did not differ significantly among the four species, but α‐amylase activity was significantly higher in the two Xiphister species, followed by C. violaceus, and then A. purpurescens. The wide disparity between the two carnivores, the striking similarity between the two sister taxa, and the significant difference between the two herbivores indicate that activity of α‐amylase follows a pattern influenced more by phylogeny than by diet in these fishes.

Morphological character variation was examined in Atherinops affinis, a temperate marine silverside with a broad geographic range and presumed limited powers of dispersal. Populations of this species were sampled from three California mainland sites, one Channel Island site and one site in the upper Gulf of California. A geometric morphometric analysis yielded higher resolution in the assessment of phenotypic divergence among the four Pacific coast populations than either body measurement or meristic analysis, and it showed that most of the shape variation among these populations occurs in the head region and body depth of the fish. All three analyses supported the hypothesis that populations of A. affinis from central and southern California coastal waters and from Santa Catalina Island are morphologically distinct from each other; the Santa Catalina Island population was found to be the most divergent. On the basis of meristic characters alone, the population of A. affinis from the upper Gulf of California was different from A. affinis populations along the Pacific coast of California. The analyses revealed variation in several morphological characters, e.g. body depth and meristics, known to vary in association with environmental conditions. Given that A. affinis appears to have low among‐population genetic variation, this species may be phenotypically plastic in response to the environmental conditions of the habitat of each population.

Brycon guatemalensis, a Neotropical characid fish, consumes an entirely terrestrial diet, shifting from eating insects as juveniles to fruits and leaves as adults. Juvenile and larger‐sized fish collected in the Rio Puerto Viejo at the La Selva Biological Station in Costa Rica were studied to test the hypotheses that, with ontogeny, (1) relative gut length increases, (2) pyloric caeca arrangement and number remain unchanged and (3) pepsin, trypsin and lipase activities decrease, while α‐amylase activity increases. These hypotheses were mainly supported in that larger fish had longer guts, unchanged pyloric caeca arrangement but fewer caeca, and, at both environmental and standard temperatures for the enzyme assays, lower pepsin and trypsin activities but higher α‐amylase activities than the juveniles. Only lipase, among the digestive enzymes, exhibited the unexpected outcome of either not differing significantly in activity (per g of tissue) between juveniles and larger fish or being significantly higher (per mg of protein) in larger fish. The overall results support the view thatB. guatemalensisis specialized morphologically and biochemically to function first as a carnivore and then as a herbivore during its life history.

Effects of variable energy intake on chick growth, organ development, and gut-passage time in seabirds were investigated by raising Elegant Tern (Sterna elegans) chicks in the laboratory on three diets involving a major prey species, northern anchovy (Engraulis mordax), and a minor prey species, topsmelt (Atherinops affinis). Anchovies are ∼25% higher in energy content than topsmelt and represent a more abundant but highly fluctuating prey resource. Chicks were raised from age 15 to age 35 days posthatch on one of three diets (n = 8): (1) high-energy anchovy at the average daily intake rate, (2) low-energy topsmelt at the same intake rate, and (3) high-energy topsmelt (i.e. at a biomass equal in energy content to the anchovy diet). Chicks raised on the high-energy anchovy diet had a significantly faster gain of body mass and wing length. All three groups, however, had attained a statistically similar wing length at 35 days posthatch and did not differ in lean dry mass or pectoral muscle mass, ind... Resumen Se estudiaron los efectos de la ingestión variable de energía sobre el crecimiento de los pichones, el desarrollo de los órganos y los tiempos de paso por el tracto digestivo de aves marinas a través de la cría de pichones de Sterna elegans en condiciones de laboratorio. Se utilizaron tres dietas incluyendo una especie de presa principal, la anchoa Engraulis mordax, y una especie de menor importancia, el pejerrey Atherinops affinis. Las anchoas tienen un contenido de energía ∼ 25% mayor que los pejerreyes y representan un recurso alimenticio más abundante, pero altamente fluctuante. Los pichones fueron criados desde el día 15 hasta el día 35 después de la eclosión con una de tres dietas: (1) anchoas de alta energía, a la tasa promedio de ingestión diaria, (2) pejerreyes de baja energía a la misma tasa de ingestión y (3) pejerreyes de alta energía (i.e. a una biomasa igual en contenido energético a la dieta de anchoas). Los pichones criados con la dieta de anchoas de alta energía aumentaron su masa...

Studies were conducted at the La Selva Biological Station in the Atlantic lowlands of Costa Rica and in a greenhouse in California to assess the potential role of a Neotropical fish in dispersing the seeds of a rain forest tree. Feeding experiments showed that the seeds of Ficus glabrata H. B. K., a major, canopy-forming riparian tree, require approximately 18–36 h to pass through the digestive tract of Brycon guatemalensis Regan, an abundant riverine fish whose adult diet consists largely of leaves and fruits of this fig tree. The seeds were still viable after passing through the fish’s gut but germinated somewhat more slowly than seeds that had been left in the fig exposed to air or floated in water. Stem elongation of seedlings from seeds that had passed through the fish’s gut was faster than that of seeds in the other two treatments. Placement of seeds upstream may be more important than enhanced germination for plants such as Ficus that produce large numbers of seeds. Radio telemetry showed that five of six tagged fish had moved distances of 0.1–1 km upstream; seven other fish with transmitters, including three large males, were not relocated and may have moved into tributary streams for spawning or feeding. These findings suggest that Brycon can disperse large numbers of Ficus seeds and help maintain the upstream populations of the tree.