Tu Tran and Dr. Mark Belk, Integrative Biology
Different selective environments could often predict life-history strategies (sensu Endler 1986). Resource levels of the environments strongly affect fitness and evolutionary stable strategies of species (Patrick and Pierre 1993). Similarly, predators also have a major effect on the life history of fish populations. The fish population from the predator’s area attained maturity at a smaller size, produced more, and smaller offspring relative to populations from predator-free environments (Johnson and Belk 2001).
In this study, I tested whether different environments can predict phenotypic life-history and growth divergence observed in the Vietnam non-livebearing fish Zenarchopterus dispar. I am interested in the unique shape of this species in the Hemiramphidae family which are characterized as having a greatly prolonged, beak-like lower jaw and short upper jaw. To date, research of this family has focused on reproduction and embryo development, or general habits. I surveyed and compared life-history of populations of Zenarchopterus dispar. By using the morphometric software and otoliths study, the specie’s phenotype and growth divergence were analyzed. This study would provide a great understanding of adaptation in the life-history phenotypes and growth of this species.
The specimens were collected over three days from May 9th to May 11th of 2008 in two areas of Dong Bo River in Khanh Hoa Province, Vietnam. Fishes were collected with dipnets. Male and female populations were determined from each of the two areas. Overall, there were 119 individuals from location 1 and 71 individuals from location 2. All fishes were humanely killed and preserved in formaldehyde in the field and were transported to the Vietnamese Oceanographic Institute for further analysis. I measured: (1) male standard length and mass at maturity; (2) female standard length and mass at maturity; (3) Embryo’s weight; (4) age as estimated from otoliths; (5) and Morphometric shape variation.
I assessed morphological shape variation of Zenarchopterus dispar among the two areas using Geometric Morphometric analysis facilitated by using the TPS series software. I took picture of each individual using a Canon SD750 digital camera and tagged all specimens with BYU official number. I would then digitize homologous the landmarks on the pictures to quantify the shape of each individual. The TPS software would align specimens and create principal component scores that would be used in multivariate analyses. Patterns of body size variation would be investigated using a Multiple Analysis of Variance (MANOVA).
The growth divergence of two populations was significant. The centroid size of male and female was statistically significant in all ANCOVA models (F< 7.041e-15). The F values indicated that there are distinct size differences between male and female (F= 11.6659), the differences among population (F=1.9305), and also the differences between young and old individuals (F= 6.5637).
This study revealed a clear association between available resources and growth divergence among the Zenarchopterus dispar populations. The high density zooplankton (prey) population at the estuary contributed to the Zenarchopterus dispar’s size development. The size differences would benefit the population toward higher survival rate and lower mortality rate. In addition, due to the current flow in the estuary, the Half-beak would swim more often against the current. This exercise contributed to fish’s characteristics as a longer and thinner body to reduce the water resistances. This characteristic was an important evolutionary step which helped this Zenarchopterus dispar population to swim faster to catch up with their prey and also to escape the predators.
Like other life-history traits, under higher predator-mediated selection at the estuary, the Zenarchopterus dispars had to disperse more energy toward reproduction rather than development. The female would mature earlier, so they could spawn more eggs. This strategy helped the population at the estuary to keep up with the reproductive allocation standard.
This study helps me grow intellectual and personal. Especially, I learned to operate research project independently include gathering data, running experiment and producing conclusion. While I was in Vietnam, I recruited fishermen to help me collecting the specimens. I operated smoothly with my cruise and balance strength and spiritual among team members. Furthermore, despite the lack of precise equipments, my data were still valuable for analysis. In addition, I had to choose Zenarchopterus dispar instead of Hemiramphus far as I proposed earlier, because the Zenarchopterus dispar was easily accessed and collected for sufficient specimens.
I have found that there are variations of phenotype within species over different selective environments; this would suggest that geographic isolation is an important factor in shaping the evolution of the Hemiramphidae. My results will give way to further research at our university as well as throughout the scientific community as this archetype can be applied to the field generally.
This project is attributed to Dr. Mark Belk. Not only did he constantly provide valuable suggestions, but he also urged me to complete this project. In addition, I appreciate the PhD candidate Josh Rasmussen, and the master student John Aedo for helping me with data interpretation and feedback.