PHD Candidate, University of Hawaii
Dispersal and Connectivity of a Hawaiian Reef Fish
In Hawaii it is estimated that 31% of the residents participate in recreational fishing (fishing for sport, leisure or subsistence). It is also estimated that 36% of the total catch for the waters surrounding Hawaii American Samoa, Guam and the Northern Mariana Islands are attributed to recreational fish harvest. Under-managed fisheries can lead to overfishing and can prohibit the long-term sustainability for communities that use this natural resource for subsistence. Maintaining food security into the future will require new management approaches to protecting coastal resources. One of the first steps to informing proper management of fisheries is to determine the source of fish populations. The purpose of my research is to track reef fishes from the site where they are produced as larvae, to the location where they settle on the reef. Ultimately, we will identify dispersal and connectivity patterns to answer the question: “Where are the fish coming from and where are they going?” It was once believed that when fish spawned their larvae floated passively with the currents. However, we now know that larvae can be selective regarding where and when they settle and understanding ocean currents alone is not sufficient to identify dispersal patterns. Similar to a paternity test, a parentage analysis will be conducted using genetic technology to link new generations of fishes (offspring) to the adults who produced them (parents). The results will identify specific areas that act as a source population that sends out larvae to replenish other areas, as well as populations that receive fish recruits. This information is essential for resolving coastal connectivity and a necessary component to identify areas that may be under fishing pressure. I will be applying this approach to a common and heavy fished species of reef fish, the Convict Tang, Acanthurus triostegus. Hawaiian community leaders have identified the Convict Tang as a species of concern and the results of this research will be presented to local leaders to help to inform community-based management efforts to sustainably manage this species. The results of my research will also be of interest to state and federal agencies. The need to understand connectivity is vital for long-term sustainability and to properly inform management strategies. This research will help ensure that Hawaiian nearshore fish populations remain healthy and sustainable by illuminating the sources of successful fish recruitment.
Abstract: The aim of this study was to resolve the evolutionary history, biogeographical barriers and population histories for sister species of wrasses, the African Coris (Coris cuvieri) in the Indian Ocean and Red Sea, and the Yellowtail Coris (Coris gaimard) in the Pacific Ocean. Glacial sea level fluctuations during the Pleistocene have shaped the evolutionary trajectories of Indo‐Pacific marine fauna, primarily by creating barriers between the Red Sea, Indian Ocean and Pacific Ocean. Here, we evaluate the influence of these episodic glacial barriers on sister species C. cuvieri and C. gaimard.Red Sea, Indian Ocean, Pacific Ocean.Sequences from mitochondrial DNA cytochrome oxidase c subunit I (COI), and nuclear introns gonadotropin‐releasing hormone (GnRH) and ribosomal S7 protein were analysed in 426 individuals from across the range of both species. Median‐joining networks, analysis of molecular variance and Bayesian estimates of the time since most recent common ancestor were used to resolve recent population history and connectivity.Cytochrome oxidase c subunit I haplotypes showed a divergence of 0.97% between species, and nuclear alleles were shared between species. No population structure was detected between the Indian Ocean and Red Sea. The strongest signal of population structure was in C. gaimard between the Hawaiian biogeographical province and other Pacific locations (COI ϕST = 0.040–0.173, P < 0.006; S7 ϕST = 0.046, P < 0.001; GnRH ϕST = 0.022, P < 0.005). Time to most recent common ancestor is c. 2.12 Ma for C. cuvieri and 1.76 Ma for C. gaimard.We demonstrate an Indian‐Pacific divergence of < 2 Myr and high contemporary gene flow between the Red Sea and Indian Ocean, mediated in part by the long pelagic larval stage. The discovery of hybrids at Christmas Island indicates that Indian and Pacific lineages have come into secondary contact after allopatric isolation. Subspecies status may be appropriate for these two wrasses.
Pub.: 01 Jan '16, Pinned: 20 Jul '17
Abstract: The drivers of speciation remain among the most controversial topics in evolutionary biology. Initially, Darwin emphasized natural selection as a primary mechanism of speciation, but the architects of the modern synthesis largely abandoned that view in favour of divergence by geographic isolation. The balance between selection and isolation is still at the forefront of the evolutionary debate, especially for the world's tropical oceans where biodiversity is high, but isolating barriers are few. Here, we identify the drivers of speciation in Pacific reef fishes of the genus Acanthurus by comparative genome scans of two peripheral populations that split from a large Central-West Pacific lineage at roughly the same time. Mitochondrial sequences indicate that populations in the Hawaiian Archipelago and the Marquesas Islands became isolated approximately 0.5 Ma. The Hawaiian lineage is morphologically indistinguishable from the widespread Pacific form, but the Marquesan form is recognized as a distinct species that occupies an unusual tropical ecosystem characterized by upwelling, turbidity, temperature fluctuations, algal blooms and little coral cover. An analysis of 3737 SNPs reveals a strong signal of selection at the Marquesas, with 59 loci under disruptive selection including an opsin Rh2 locus. While both the Hawaiian and Marquesan populations indicate signals of drift, the former shows a weak signal of selection that is comparable with populations in the Central-West Pacific. This contrast between closely related lineages reveals one population diverging due primarily to geographic isolation and genetic drift, and the other achieving taxonomic species status under the influence of selection.
Pub.: 11 Mar '15, Pinned: 20 Jul '17
Abstract: Ecological communities that occupy similar habitats may exhibit functional convergence despite significant geographical distances and taxonomic dissimilarity. On coral reefs, steep gradients in key environmental variables (e.g. light and wave energy) restrict some species to shallow depths. We show that depth-generalist reef fishes are correlated with two species-level traits: caudal fin aspect ratio and diet. Fishes with high aspect ratio (lunate) caudal fins produce weaker vortices in the water column while swimming, and we propose that 'silent swimming' reduces the likelihood of detection and provides an advantage on deeper reefs with lower light irradiance and water motion. Significant differences in depth preference among trophic guilds reflect variations in the availability of different food sources along a depth gradient. The significance of these two traits across three geographically and taxonomically distinct assemblages suggests that deep-water habitats exert a strong environmental filter on coral reef-fish assemblages.
Pub.: 23 Jan '16, Pinned: 20 Jul '17
Abstract: The regal angelfish (Pygoplites diacanthus; family Pomacanthidae) occupies reefs from the Red Sea to the central Pacific, with an Indian Ocean/Rea Sea color morph distinct from a Pacific Ocean morph. To assess population differentiation and evaluate the possibility of cryptic evolutionary partitions in this monotypic genus, we surveyed mtDNA cytochrome b and two nuclear introns (S7 and RAG2) in 547 individuals from 15 locations. Phylogeographic analyses revealed four mtDNA lineages (d = 0.006 – 0.015) corresponding to the Pacific Ocean, the Red Sea, and two admixed lineages in the Indian Ocean, a pattern consistent with known biogeographical barriers. Christmas Island in the eastern Indian Ocean had both Indian and Pacific lineages. Both S7 and RAG2 showed strong population-level differentiation between the Red Sea, Indian Ocean, and Pacific Ocean (ΦST = 0.066 – 0.512). The only consistent population sub-structure within these three regions was at the Society Islands (French Polynesia), where surrounding oceanographic conditions may reinforce isolation. Coalescence analyses indicate the Pacific (1.7 Ma) as the oldest extant lineage followed by the Red Sea lineage (1.4 Ma). Results from a median-joining network suggest radiations of two lineages from the Red Sea that currently occupy the Indian Ocean (0.7 – 0.9 Ma). Persistence of a Red Sea lineage through Pleistocene glacial cycles suggests a long-term refuge in this region. The affiliation of Pacific and Red Sea populations, apparent in cytochrome b and S7 (but equivocal in RAG2) raises the hypthosis that the Indian Ocean was recolonized from the Red Sea, possibly more than once. Assessing the genetic architecture of this widespread monotypic genus reveals cryptic evolutionary diversity that merits subspecific recognition.
Pub.: 08 Apr '16, Pinned: 20 Jul '17
Abstract: Hybridization in the ocean was once considered rare, a process prohibited by the rapid evolution of intrinsic reproductive barriers in a high-dispersal medium. However, recent genetic surveys have prompted a reappraisal of marine hybridization as an important demographic and evolutionary process. The Hawaiian Archipelago offers an unusual case history in this arena, due to the recent arrival of the widely distributed Indo-Pacific sergeant (Abudefduf vaigiensis), which is hybridizing with the endemic congener, A. abdominalis. Surveys of mtDNA and three nuclear loci across Hawai'i (N = 396, Abudefduf abdominalis and N = 314, A. vaigiensis) reveal that hybridization is significantly higher in the human-perturbed southeast archipelago (19.8%), tapering off to 5.9% in the pristine northwest archipelago. While densities of the two species varied throughout Hawai'i, hybridization was highest in regions with similar species densities, contradicting the generalization that the rarity of one species promotes interspecific mating. Our finding of later generation hybrids throughout the archipelago invokes the possibility of genetic swamping of the endemic species. Exaptation, an adaptation with unintended consequences, may explain these findings: the endemic species has transient yellow coloration during reproduction, whereas the introduced species has yellow coloration continuously as adults, in effect a permanent signal of reproductive receptivity. Haplotype diversity is higher in Hawaiian A. vaigiensis than in our samples from the native range, indicating large-scale colonization almost certainly facilitated by the historically recent surge of marine debris. In this chain of events, marine debris promotes colonization, exaptation promotes hybridization, and introgression invokes the possible collapse of an endemic species.
Pub.: 07 Oct '14, Pinned: 20 Jul '17