A multi-locus genetic assignment technique to assess ... - CiteSeerX

Marine Biology (2005) 147: 1141–1148 DOI 10.1007/s00227-005-0022-5

R ES E AR C H A RT I C L E

Daniel A. Brazeau Æ Paul W. Sammarco Daniel F. Gleason

A multi-locus genetic assignment technique to assess sources of Agaricia agaricites larvae on coral reefs

Received: 10 February 2004 / Accepted: 5 April 2005 / Published online: 13 July 2005
Springer-Verlag 2005

Abstract Assignment of individuals to populations based upon genetic data is an important ecological problem that requires many polymorphic markers, often more than are available using single locus techniques. To demonstrate the utility of amplified fragment length polymorphisms (AFLP) in studying larval dispersal and recruitment in coral populations, two sets of AFLP primers were used to genotype colonies of the coral Agaricia agaricites Linnaeus from three widely separated geographic locations: the Bahamas (2328¢N, 7542¢W) and Key Largo, Florida (2455¢N, 8031¢W—two sites separated by 12 km) in 1995, and the Flower Garden Banks (FGB) in the Gulf of Mexico (2755¢N,9336¢W) in 1997. In addition to adult samples from each site, recruits were collected from settling plates placed on the East FGB for 1 year (1997–1998). The AFLP technique yielded 45 polymorphic markers. An analysis of molecular variance (AMOVA) showed significant genetic differences among the four adult populations, even between the two Key Largo sites. The recruits were significantly different from all adult populations except those from the FGB. Discriminant function analysis and the program AFLPOP were used to assign individuals to populations. Using the adult AFLP-banding patterns to build the statistical models, both procedures correctly Electronic Supplementary Material Supplementary material is available for this article at http://dx.doi.org/10.1007/s00227-0050022-5 Communicated by J.P.Grassle, New Brunswick D. A. Brazeau (&) Department of Pharmaceutical Sciences, University at Buffalo, Buffalo, NY 14260-1200, USA E-mail: dbrazeau@buffalo.edu Fax: +1-716-6453693 P. W. Sammarco Louisiana Universities Marine Consortium (LUMCON), 8124 Hwy. 56, Chauvin, LA 70344, USA D. F. Gleason Department of Biology, Georgia Southern University, Statesboro, GA 30460-8042, USA

assigned the majority of adults to their respective populations in simulations and assigned all but one of the recruits to the Flower Garden population from where they were collected. The AFLP technique provides a simple and adaptable population assignment method for studying recruitment processes in A. agaricites and other coral species.

Introduction Understanding factors that affect recolonization of reefs by coral larvae is essential for predicting reef recovery and persistence. In particular, understanding whether planulae that settle on a reef are derived primarily from local adult populations or from more distant populations is critical to understanding the ability of coral populations to recover from environmental perturbations (Bak and Engel 1979; Carlon and Olson 1993; Sammarco 1996; Roberts 1997; Cowen et al. 2000; Swearer et al. 2002). In sessile epibenthic organisms such as scleractinian corals, migration among populations is largely the result of dispersal of planktonic larvae. Thus, the diversity of reproductive strategies observed in corals affects not only patterns of dispersal but also determines in part the genetic structure of coral populations (Stoddart 1984a, b; Ayre and Resing 1986; Ayre and Dufty 1994; Brazeau and Harvell 1994; Ayre et al. 1997a). For example, coral species with internal fertilization that brood their larvae may tend to self-seed their own (natal) reefs (Sammarco and Andrews 1988). Those that have external fertilization (broadcasters) and planktonic larval development may do little self-seeding, since planktonic larvae generally spend more time in the water column, allowing for greater dispersal (Sammarco and Andrews 1988, 1989; see Harrison and Wallace 1990; Sammarco 1994 for general discussions). These general assumptions require further testing since some species have larvae that settle and metamorphose after only 2–3 days, thus allowing for potential self-seeding of

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reef populations for these species (Miller and Mundy 2003). Analyses of the genetic markers in the Indo-Pacific species Pocillopora damicornis with a nested design suggest that both local (within reef, 90% correct classification for the two Key Largo populations (Table 2). Each Key Largo population had one individual incorrectly assigned to the other Key Largo population. Classification of the recruits using the discriminate function model based upon adults resulted in 10 of the 11 being assigned with high probability (P>0.995) to the Flower Garden population, one individual was assigned with marginal

Fig. 2 Plot of each coral sample based upon canonical scores. Bahamas dark circles, Conch Reef dark triangles, Crocker Reef light triangles, Flower Gardens light circles, and recruits squares

probability (P=0.75), and the remaining individual was assigned to Crocker Reef with a probability of P=0.82. The close genetic similarity between the recruits and the Flower Garden adults can also be seen in the plot of canonical scores (Fig. 2). Results from the AFLPOP program were concordant with the DFA. The AFLPOP procedure uses all the band data rather than a subset of the data as is the case for DFA. Using AFLP band frequencies the majority of adults from each population were assigned to their respective populations, though not as well as with the DFA (Table 3). As with the DFA, the majority of misassignments were between the two Florida Keys populations. Using an assignment threshold of 1.0 resulted in fewer incorrect assignments with an increase in cases in which no assignment could be made. For the recruit assignments, AFLPOP assigned all of the recruits to the Flower Garden population.

Discussion The AFLP technique yielded 45 scorable polymorphic markers for A. agaricites. One could potentially obtain

Table 1 Agaricia agaricites. Assessment of genetic differentiation among populations using analysis of molecular variance (AMOVA) Bahamas Bahamas Conch Reef Crocker Reef Flower Gardens Recruits

0.074 0.116 0.100 0.096

Conch Reef

Crocker Reef

Flower Gardens

Recruits

P