Taxonomic implications
Our two starting hypotheses explained the reported lack of sorting in
mitochondrial and nuclear genes among nominal species, either as a
single species exhibiting extreme morphological polymorphism or as two
nominal species with restricted hybridisation between them. Instead, our
results support the existence of a third lineage, along with H.
maderiana and H. insularum MDB, consisting of the individuals
from Porto Santo initially assigned to H. insularum . Hence, the
fuzzy boundaries between the species would be due to incomplete lineage
sorting. Interestingly, H. insularum exhibits intraspecific
variation in shape and size across the islands
(Crespo et al., 2022), which
led Wunderlich (1992) to describe the species H. biscoitoi Wunderlich, 1992, based on specimens from Porto Santo. Subsequently,
Crespo et al. (2022) proposed H. biscoitoi as a junior synonym ofH. insularum due to the lack of diagnostic morphological features
and genetic distinctiveness. The lack of diagnostic features amongH. insularum specimens from different island populations
(Madeira, Desertas, Bugio and Porto Santo), with only minor variations,
could also be attributed to homogeneous genetic variation caused by
incomplete lineage sorting. This process can preserve symplesiomorphic
morphological states, as suggested by
(Futuyma, 2010). Crespo et
al. (2022) further proposed the existence of a phenotypic continuity
between the two extremes represented by the nominal species H.
maderiana or H. insularum . Notably, most specimens with
intermediate size and/or yellowish pilosity on the anterior legs, found
in Porto Santo, correspond to H. maderiana, as also recovered in
our results. Unfortunately, the limited sample of specimens from the
different islands prevented us from conducting quantitative
morphological analyses to further test the morphological distinctiveness
of the island populations of H. insularum.
The rejection of gene flow across the different species in our MadeiranHogna is surprising, given that recent studies have revealed the
key role of gene flow between islands in promoting habitat adaptation inHogna species on the Galapagos Islands
(De Busschere et al., 2015).
In this regard, wolf spiders are well-reputed for their great ability
for long-distance dispersal
(Bonte et al., 2006;
Dries & Maelfait, 2001), as already illustrated by the presence ofH. insularum in multiple islands. A possible explanation for the
lack of hybridisation, or even a potential driver of speciation in our
model system, could be found in the complex courtship behaviour
exhibited by wolf spiders, which has frequently been used to diagnose
species (Chiarle et al.,
2013; Just et al., 2019). Although little is known about the courtship
behaviour of Madeiran Hogna , the species pair H. maderiana and H. insularum differ in traits related to male signalling
during courtship displays. Specifically, H. maderiana has
pedipalps and front legs conspicuously marked in orange, which are
absent in H. insularum . The absence of gene flow or hybridisation
events in Hogna speciation may hint at the development of
specific courtship behaviours during mating, which prevents genetic
material from crossing between species and could promote speciation in
Madeiran Hogna.