3.1. Population/Islet genetic diversity
Genetic diversity based on the COMBINED dataset is summarized in Figure 3. While diversity statistics for the individual datasets (GBS and RADSeq) was slightly higher in the absolute estimates per locality (Table S3), the relative pattern found among localities was highly preserved, indicating that the reduced COMBINED dataset is overall representative of the relative genetic diversity within this species.
Population nucleotide diversity (Pi) ranged between 0.104 and 0.174, with the three archipelagos showing similar ranges: 0.123- 0.156 (Cabrera), 0.109-0.174 (Mallorca) and 0.104-0.158 (Menorca) (Figure 3). The observed heterozygosity (Ho) showed comparable values as Pi, varying between 0.095 and 0.140. Most diverse populations/islets per archipelago were the two Cabrera localities (Cabrera), Guardia and Moltona (Mallorca), and Aire and Colom (Menorca); the least diverse populations were the small islets of Porros (Menorca), Colomer (Mallorca) and Esclatasang (Cabrera) (Figure 3). Fis values were positive for all populations and range from 0.009 (Porros) to 0.107 (Moltona), indicating low inbreeding effect despite the small size of some islands. Individual datasets (GBS and RADSeq) based on a more extensive number of SNPs confirmed low Fis values and major trend among populations (Table S3). The Allelic richness (Ar) was also comparable across localities, ranging between 1.245 (Porros) and 1.438 (Dragonera). The number of private alleles (PA) estimated on individual datasets (Table S3) vary greatly, with highest values found in the four smallest islets of Porros, en Curt, Esclatasang and Foradada (n>1000, island area < 1.50 ha), with the small islet of en Curt presenting the largest number (n=5316) (Table S3).
Of the genetic diversity indexes, Ar, Pi and Fis showed positive coefficients with the islet surface and negative with maximum altitude in multiple regression models (Ar: p<0.001 only for Area, Pi: p=0.001 for Area and p<0.005 for Max altitude, Fis: p<0.05 for Area and Max altitude), indicating that the smallest islets typically host a more reduced genetic diversity, although no evident inbreeding depression.