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.