Saillant and Gold: Population structure and variance effective size of Lul/anus campechanus in the northern Gulf of Mexico 



139 



Significant heterogeneity (exact tests) among samples 

 in either allele or genotype distributions (or both) was 

 found overall and, after Bonferroni correction, at four 

 individual microsatellites (Table 1). Pairwise compari- 

 sons (exact tests) of allele and genotype distributions 

 between samples paralleled one another and revealed 

 that almost all of the genetic heterogeneity was due 

 to the 1995 cohort from Texas and the 1997 cohort 

 from Alabama (Table 2). This result indicated that the 

 observed genetic heterogeneity is more temporal (be- 

 tween cohorts) than spatial (among localities). Temporal 

 rather than spatial heterogeneity also was indicated by 

 the nonsignificant exact tests among localities sampled 

 in 1997 and by the average Fgj values among localities 

 (both cohorts) of less than 0.001. 



Results of assignment tests are given in Table 3. On 

 average, 53% of the individuals were "assigned" (i.e., 

 had the highest probability of belonging) to their origi- 

 nal locality. This proportion was significantly higher 

 (P<0.001) than that expected if multilocus genotypes 

 were distributed randomly with respect to geographic 

 location. However, the estimated probabilities of be- 

 longing to all three localities were higher than 0.05 for 

 96.4-99.8% of the individuals, indicating that none of 

 the three localities could be rejected as a potential ori- 



Table 2 



Pairwise F^-j. values (upper diagonal) and probability 

 that F^j.=0 (lower diagonal) for twelve samples (four 

 cohortsxthree localities) of red snapper iLutjanus cam- 

 pechanus) from the northern Gulf of Mexico. Boldface 

 indicates significance following sequential Bonferroni 

 correction. TX=Texas; LA=Louisiana; AL-Alabama. 



TX95 LA 95 AL 95 TX 97 LA 97 AL 97 



TX95 

 LA 95 

 AL95 

 TX97 

 LA 97 

 AL97 



0.002 

 0.001 

 0.000 



0.036 

 0.000 



0.0012 



0.031 

 0.013 

 0.756 

 0.000 



0.0010 

 0.0006 



0.001 



0.737 

 0.000 



0.0013 

 0.0007 

 0.0008 



0.079 

 0.045 



0.0010 0.0020 

 -0.0002 0.0009 

 -0.0001 0.0015 



0.0005 0.0002 

 — 0.0006 



0.073 — 



Table 4 



Estimates of variance effective size (N^,y) and 95*^ confi- 

 dence intervals for red snapper iLutjaniis campechanus) 

 sampled at three geographic localities in the northern 

 Gulf of Mexico. Estimates were generated using the 

 pseudo-maximum-likelihood method of Wang (20011. Val- 

 ues are corrected for overlapping generations, following 

 Jorde and Ryman (1995). 



Locality 



Af., 



95% lov 



95<>r high 



6.52 

 3275 



777 



2706 



>75,000 



2515 



gin. In addition, for four individuals from the Alabama 

 sample (0.6%), all three localities were excluded as the 

 potential origin. 



The pseudo-maximum-likelihood (temporal-method) 

 estimates of variance effective size (N^y), corrected for 

 overlapping generations, and their 95% confidence in- 

 tervals for all three localities are shown in Table 4. 



