Quantification of whole brain arginine vasotocin for two Syngnathus pipefishes: elevated concentrations correlated with paternal brooding.

Arginine vasotocin (AVT) regulates many aspects of fish physiology and behavior including courtship and reproduction. This study begins to address whether paternal functions for AVT have independently evolved in species in which paternal behavior has evolved. We quantified AVT in the brains of Syngnathus fuscus and Syngnathus floridae which, like other pipefishes and seahorses of the family Syngnathidae, brood embryos within specialized structures of the male. For both species, we measured AVT concentrations seventeenfold higher for some males during brooding compared to post-brooding males. Comparable whole brain AVT concentrations between gravid females and males with broods at some embryonic development stages suggest physiological similarities that we hypothesize is related to nutrient provisioning but should be elucidated with further studies including a detailed anatomical analysis of AVT production. Earlier studies have identified differences in the brooding structures of these species. Here we documented interspecific differences in the variability and mean AVT concentration for non-brooding males, the brood stage showing a return to post-brooding concentrations, and the variability of AVT concentrations for brooding males with embryos in some development stages. Future investigations should use these data to investigate the potential for divergent AVT function between species, sexes, and brooding males with embryos of different developmental stages.

Elevated whole brain arginine vasotocin with Aroclor 1254 exposure in two Syngnathus pipefishes.

The neurohypophysial hormone arginine vasotocin (AVT) and the neuroendocrine system strongly interact with the rest of the teleostean endocrine system. The aim of this study is to investigate the effects of exposure to an endocrine disruptor on whole brain AVT concentrations for the pipefishes Syngnathus floridae and S. fuscus. Following treatment over the entire brood period, AVT concentrations were significantly higher for Aroclor 1254-exposed, post-brooding males compared to controls for both species. Considering both previously documented seventeen-fold increases in AVT for brooding males with embryos in some developmental stages and changes in parental nutrient concentrations after Aroclor 1254 exposure, these data begin to address potential physiological mechanisms that may underlie paternal activities in syngnathid males.

Osmoregulatory role of the paternal brood pouch for two Syngnathus species.

Even though sea horses, sea dragons, and pipefishes of the teleost family Syngnathidae have been studied for over a century, the physiological significance of the paternal brood pouch is not well defined. Here we document the regulation of brood pouch osmolality during embryonic development for Syngnathus floridae and Syngnathus fuscus, particularly during the middle brood stages or around hatching. S. fuscus brood pouch osmolality was significantly lower than non-brooding conspecifics for all brood stages, but early and late stage S. floridae displayed pouch osmolality comparable to non-brooding males, suggesting brood pouch osmoregulation at these stages may be important for S. fuscus embryonic development. Quantification of Na(+), K(+), Ca(2+), and Mg(2+) in paternal blood plasma, pouch fluid, and embryos indicated that regulation of these ions contributes to pouch osmoregulation and furthermore, that ions in the brood pouch are most likely derived from the environment and not paternal blood. While both species displayed significant increases in dry mass and changes in embryonic ion concentrations during development, net uptake of paternally-derived ions was not documented. Overall, this examination furthers our understanding of syngnathid brood pouch physiology and offers insight into the evolution of paternal care in these fishes.

Direct evidence for embryonic uptake of paternally-derived nutrients in two pipefishes (Syngnathidae: Syngnathus spp.).

Seahorses, sea dragons and pipefishes of the teleost family Syngnathidae are unique in that embryos develop within specialized brooding structures of the male. We enriched brooding Syngnathus fuscus and Syngnathus floridae males with injections of L-lysine-[(15)N(2)] and 16:0-palmitic acid 1-[(13)C] to demonstrate embryonic uptake of paternally-derived nutrients. While all embryos demonstrated amino acid enrichment, late stages showed significantly higher [(15)N], indicating greater utilization of paternal resources as yolk reserves diminished and embryonic energy demands increased. Limited embryonic [(13)C] uptake, defined as less than 10% of adult enrichment, in 75 and 81% of S. floridae and S. fuscus respectively signified rapid lipid metabolism and thus the need for greater enrichment. Interspecific differences in embryonic uptake of paternally-derived nutrients were not demonstrated. However, interspecific differences in egg nutrient reserves and fry size but comparable fry nutrient levels along with data from a published paternal exposure study indicate paternal transfer in S. fuscus most likely compensates for the comparative egg nutrient deficiency. This study is the first to our knowledge to provide direct evidence for the functional significance of the brood pouch in nutrient provisioning. These results add comparative information on the diversity of Syngnathid paternal care and further our understanding of paternal influence on development.

Influence of estuarine hypoxia on feeding and sound production by two sympatric pipefish species (Syngnathidae).

This research utilizes the acoustic behavior of two sympatric pipefish species to assess the impact of hypoxia on feeding. We collected northern, Syngnathus fuscus, and dusky pipefishes, Syngnathus floridae, from the relatively pristine Chincoteague Bay, Virginia, USA and audiovisually recorded behavior in the laboratory of fish held in normoxic (>5 mg/L O(2)) and hypoxic (2 and 1 mg/L O(2)) conditions. Both species produced high frequency ( approximately 0.9-1.4 kHz), short duration (3-22 msec) clicks. Feeding strikes were significantly correlated with both wet weight of ingested food and click production. Thus, sound production serves as an accurate measure of feeding activity. In hypoxic conditions, reduced food intake corresponded with decreased sound production. Significant declines in both behaviors were evident after 1 day and continued as long as hypoxic conditions were maintained. Interspecific differences in sensitivity were detected. Specifically, S. floridae showed a tendency to perform head snaps at the surface. S. fuscus exhibited a breakdown in the coupling of sound production with food intake in 2 mg/L O(2) with clicks produced in other contexts, particularly choking and food expulsion. Reductions in feeding will ultimately impact growth, health, and eventually reproduction as resources are devoted to survival instead of gamete production and courtship. This work suggests acoustic monitoring of field sites with adverse environmental conditions may reflect changes in feeding behavior in addition to population dispersal.

Differential parental nutrient allocation in two congeneric pipefish species (Syngnathidae: Syngnathus spp.).

Male seahorses and pipefishes of the family Syngnathidae are heralded for their unique brood pouch structures for incubating embryos. There are three general types of brood pouch with increasing complexity: simple ventral gluing, two pouch flaps and a completely sealed sac. The diversity of functional roles within a type in providing nutrition, aeration and protection to offspring is unknown. Here we reveal significant differences in parental nutrient allocation to embryos for two closely related, sympatric pipefishes with similar brood pouch structure. We document differences in embryo attachment, depletion of pouch fluid nutrients over development and egg nutrient partitioning between Syngnathus floridae and Syngnathus fuscus. In S. fuscus, females produce nutritionally poor eggs and the males implant developing embryos in the brood pouch adjacent to blood vessels. A female-biased breeding population was observed, supporting the hypothesis that the cost of male parental care is high in this species. The loose connection between eggs and brood pouch tissues and the appearance of undeveloped eggs and lipid droplets in the pouch of S. floridae males suggest this species utilizes nutrient-rich eggs produced by females as nurse eggs to supplement embryonic development. A balanced sex-ratio for S. floridae further supports more equal parental contribution. This comparison provides evidence of a decline in female gametic investment and reveals the rapid diversification of syngnathid brood pouch function. Our results indicate gross classification of brooding structures into one of the three general pouch types does not predict the energetic investment of males in parental care. But rather, physiological characterization of the relative investment by each sex to offspring is essential to understanding the functional significance of the brood pouch.