Comparison to other invasive starling populations
By comparing the three sites of invasive starling populations:
Australia, South Africa and North America, we are able to begin to
define the differences that have occurred in these three individual
introductions. The F ST values show that
Australian and South African populations are most differentiated from
one another, Australian and North American populations are moderately
differentiated, while South African and North American populations are
most similar (Table S2). This is likely due to differences in timing,
random sampling from the native range and number of introduction
attempts across these three localities, with the Australian introduction
occurring earlier than the others and characterized by multiple
attempts.
As expected, the invasive populations had lower diversity than the
native range, likely caused by genetic bottlenecks at introduction. The
highest haplotype diversity and richness is found in the UK (0.954,
30.0), although only 45 individuals were sampled, we found 26
haplotypes. Of the three introduced ranges, the haplotype diversity and
richness values are highest in North America (0.884, 14.6) and lowest
for the Australian population (0.713, 7.7). The North American
population has 17 unique haplotypes, the South African population has 14
unique haplotypes, and the Australian population has 10 unique
haplotypes. The North American population had the highest number of
novel haplotypes despite having a smaller founding size than Australia
and the smallest sample size in this study (Table 2).
Opposite to the patterns we observe with haplotype diversity, nucleotide
diversity (π) in the three invasive populations is highest in the
Australian population and the lowest in the North American population.
This could be caused by several factors. Firstly, the Australian
population is the result of multiple introductions that began earlier
than the other introductions (Jenkins, 1977). Multiple introductions
could have brought haplotypes which are differentiated from one another
by more nucleotide differences than haplotypes that evolved recently
from a single small founding population. Secondly, there is evidence of
selection on the mtDNA of the Australian population, which would have
driven certain haplotypes to higher frequencies and eliminated others
(Rollins et al. 2016). If the Australian population was originally
propogated with more nucleotide diversity than the others, selection
could explain the pattern of lower haplotype diversity evident today.
Lastly, the sample size for the Australian data was 549, for South
Africa 219 and for North America only 95 (Table 2). Therefore, although
the nucleotide diversity indicates that Australian population has the
most genetic diversity, it could be the result of the disparity in
sample sizes between the three data sets here.