Population-genetic divergence of a diplopod in a Mediterranean microsite at Mount Carmel, Israel

The differences in genetic diversity in the diplopod Tetrarthrosoma syriacum (Diplopoda, Strongylosomatidae) were tested between climatically contrasting slopes at a Mediterranean microsite in Nahal Oren, Mt. Carmel, Israel. Nahal Oren gorge consists of two opposing slopes, 200 metres apart at the bottom, varying considerably in microclimate, flora and fauna. The south-facing slope (S-slope) receives greater radiation and is warmer, drier and climatically more variable than the north-facing slope (N-slope), which is wetter, cooler, and climatically more constant. We examined 105 individuals of T. syriacum from 3 stations (1-3) on the S-slope and 105 individuals from 3 stations (4-6) on the N-slope, each tested for 9 allozyme polymorphic putative loci. The results indicated: (1) Genetic diversity indices across all 6 stations are as follows: Mean number of alleles per locus, A = 3.1 (range, 3.0-3.3), heterozygosity, H = 0.233 (range, 0.164-0.271) and gene diversity, He = 0.442 (range, 0.429-0.465); (2) A and H were higher on the S as compared to the N-slope, as predicted. The estimates of A, H and He (unbiased estimates) were on the S/N slopes as follows: 3.23/3.03; 0.248/0.218; 0.441/0.442. We also found significant overall deficiency of heterozygotes in all samples, with a tendency to higher deviation on the N-slope (Fis = 0.541) as compared to the S (Fis = 0.422). We tested the distribution of H, He, A and Fst variability 1) over all samples, 2) over each slope and 3) in pairwise comparison of neighbor stations and stations on opposite slopes. The S(1-3) + N(4) samples cluster together as to N(5) + N(6). This pattern is significantly reflected by the distribution of H, Fst, and is also idicated by genetic distance indices D by cladograms. Our results suggest a more island structure of T. syriacum on the N-slope where animals are far scarcer than on the S-slope and the divergence between the slopes may support the niche-width variation hypothesis.