Green, Bridget Siobhan (2004) Parental and environmental effects on the early life history of a tropical reef fish, Amphiprion melanopus. PhD thesis, James Cook University.

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Abstract

Tropical coral reef fish larvae are characterised by high mortality, which is predominantly driven by size- and growth- selective processes. While recent studies of environmental correlates have explained 7 - 36 % of the variation in larval growth rate in wild populations, the majority of the variation in growth rate and recruitment remains unexplained. This thesis used a series of laboratory experiments to assess the contribution of environmental and parental influences on embryonic, larval and juvenile growth and development in a tropical marine fish species, Amphiprion melanopus (Pomacentridae). Maternally determined egg size coupled with clutch micro-environment was important in determining initial offspring size. By sampling embryos and larvae for morphometric measurement and metabolic rate, we found that size differences between offspring within a clutch were related to the clutch design. Eggs on the periphery of newly laid clutches were 2% smaller than eggs from the centre, and this size difference increased throughout embryonic development. Larvae hatched from the clutch periphery were 6 – 8 % smaller than larvae hatched from the clutch centre. Embryos on the clutch periphery had 63 % lower rates of oxygen consumption. Changes in oxygen consumption throughout development were related to developmental changes within the embryo. Given that the study species, like many demersal spawning fishes, has parental care of the eggs, we explored whether parental tending modified the oxygen microenvironment of the embryos, and subsequently, whether tending was modified according to ambient dissolved oxygen (DO), increasing metabolic demands of developing embryos and water temperature. There was a time lag of 1 second between fanning and increases in the amount of oxygen within the nest, demonstrating that DO is directly affected by parental tending. Males invested more time tending nests (40 % initially) than did females (20 – 30 %), and male investment increased to 70 % as embryo development progressed. Additionally, male fish adjusted fanning effort on a diel cycle as ambient DO fluctuated. The female’s investment in nest tending was minor in comparison to the males and did not change with ontogeny, with the exception of a small increase in activity just prior to hatching. Nest tending appears to be an important mechanism whereby males can invest in the survival of their offspring. To determine the relative importance of maternal, paternal and environmental (specifically temperature) influences on early life history traits, we experimentally examined their interactive influences on larval growth, swimming ability and developmental rate using a full factorial (diallel) breeding design. There were strong paternal and maternal influences in size at hatching and metamorphosis, and surprisingly, paternal affects were responsible for 52 % of the variation in growth rate, while 30 % was attributable to the combination of temperature*female*male. We speculate this was due to the significant male contribution through their key role in nest tending. Pre-hatch egg size, post-hatching larvae size and size at metamorphosis all showed significant influences from male and female, and the interaction of these, while temperature had minimal influences on size at particular development stages. Temperature did, however, reduce developmental rate, increasing the time taken to reach metamorphosis by 50%. Larvae reared in water 25 ºC (3 ºC below ambient) were smaller than larvae reared at ambient temperature (28 ºC) at the same age (7 days after hatching, dah), and had slower critical swimming performance but took longer to metamorphose (mean: 8.9 ± 0.06 days at 28 ºC and 11.6 ± 0.09 days at 25ºC). When this slower developmental time was factored in to size and swimming, fish reared at 25 ºC were larger at similar developmental age (11dah, pre-metamorphosis). This stage-specific size increase did not result in better performance as there was no difference in swimming ability immediately prior to settlement (11dah), despite slower swimming for larvae raised at 25 °C, 7dah. This thesis shows that position of an embryo within a clutch, maternally- determined egg size and subsequent parental care were important in influencing the condition and performance of marine fish embryos and larvae. Size advantages began in the embryonic stage due to maternal investment through gametogenesis and the allocation of endogenous reserves to the egg, and were enhanced throughout development. This thesis suggests that parental contributions to the embryo were important to size, growth and performance of larvae, and may be the source of previously unexplained variation in larval growth and survival.

Item ID:	68
Item Type:	Thesis (PhD)
Keywords:	Amphiprion melanopus, Pomacentridae, Embryonic growth, Larval growth, Juvenile growth, Environmental influences, Parental influences, Life history
Date Deposited:	03 Aug 2006
FoR Codes:	06 BIOLOGICAL SCIENCES > 0602 Ecology > 060205 Marine and Estuarine Ecology (incl Marine Ichthyology) @ 50% 06 BIOLOGICAL SCIENCES > 0608 Zoology > 060801 Animal Behaviour @ 50%
SEO Codes:	96 ENVIRONMENT > 9605 Ecosystem Assessment and Management > 960506 Ecosystem Assessment and Management of Fresh, Ground and Surface Water Environments @ 100%
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