Multilocus and morphological analysis of south‐eastern Iberian Wall lizards (Squamata, Podarcis )

Signalling on islands: the case of Lilford’s wall lizard (Podarcis lilfordi gigliolii) from Dragonera

Studies of the effects of insularity on animal signals are scarce, particularly in lizards. Here, we use Lilford’s wall lizard from Dragonera (Podarcis lilfordi gigliolii) to ask how island conditions have affected its repertoire of social signals, focusing on two visual signals shared by many Podarcis species: ultraviolet (UV)–blue-reflecting ventrolateral colour patches and visual displays. We examined whether the number or spectral characteristics of the UV–blue patches are associated with traits related to individual quality. We also used visual models to assess visual conspicuousness and to measure sexual dichromatism. We did not observe foot shakes or any other visual displays usually found in continental Podarcis. We found that none of the UV–blue patch variables covaried with morphometric variables indicative of fighting ability or body condition in males, suggesting that this coloration does not signal individual quality. We also found very little sexual dichromatism. In particular, the UV–blue patches of females seem over-expressed and more similar to those of males than those of continental Podarcis. Ancestral state reconstruction reveals that the lack of sexual dimorphism in the UV–blue patches is a derived condition for P. lilfordi gigliolii and other Podarcis living on small islands. Our results thus show a pattern of reduced social signalling in P. lilfordi gigliolii relative to mainland Podarcis, with some signals being lost or under-expressed (visual displays) and others losing their signalling function (UV–blue patches). We hypothesize that these changes are attributable to the high population density of P. lilfordi gigliolii, which discourages territorial behaviour and promotes extreme social tolerance, making most social signals unnecessary. More work will be needed to determine whether this is a common pattern in lizards inhabiting small and densely populated islands.

Identification of morphologically cryptic species with computer vision models: wall lizards (Squamata: Lacertidae: Podarcis) as a case study

Automated image classification is a thriving field of machine learning, and various successful applications dealing with biological images have recently emerged. In this work, we address the ability of these methods to identify species that are difficult to tell apart by humans due to their morphological similarity. We focus on distinguishing species of wall lizards, namely those belonging to the Podarcis hispanicus species complex, which constitutes a well-known example of cryptic morphological variation. We address two classification experiments: (1) assignment of images of the morphologically relatively distinct P. bocagei and P. lusitanicus; and (2) distinction between the overall more cryptic nine taxa that compose this complex. We used four datasets (two image perspectives and individuals of the two sexes) and three deep-learning models to address each problem. Our results suggest a high ability of the models to identify the correct species, especially when combining predictions from different perspectives and models (accuracy of 95.9% and 97.1% for females and males, respectively, in the two-class case; and of 91.2% to 93.5% for females and males, respectively, in the nine-class case). Overall, these results establish deep-learning models as an important tool for field identification and monitoring of cryptic species complexes, alleviating the burden of expert or genetic identification.

Nuclear phylogenies and genomics of a contact zone establish the species rank of Podarcis lusitanicus (Squamata, Lacertidae)

Unravelling when divergent lineages constitute distinct species can be challenging, particularly in complex scenarios combining cryptic diversity and phylogenetic discordances between different types of molecular markers. Combining a phylogenetic approach with the study of contact zones can help to overcome such difficulties. The Podarcis hispanicus species complex has proven to be prosperous in independent evolutionary units, sometimes associated with cryptic diversity. Previous studies have revealed that one of the species of this complex, P. guadarramae, comprises two deeply divergent yet morphologically indistinguishable evolutionary units, currently regarded as subspecies (P. g. guadarramae and P. g. lusitanicus). In this study we used molecular data to address the systematics of the two lineages of Podarcis guadarramae and the closely related P. bocagei. Firstly, we reconstructed the species tree of these three and two additional taxa based on 30 nuclear loci using the multispecies coalescent with and without gene flow. Secondly, we used SNPs obtained from RADseq data to analyze the population structure across the distribution limits P. g. lusitanicus and P. g. guadarramae, and for comparison, a contact zone between P. bocagei and P. g. lusitanicus. Nuclear phylogenetic relationships between these three taxa are clearly difficult to determine due to the influence of gene flow, but our results give little support to the monophyly of P. guadarramae, potentially due to a nearly simultaneous divergence between them. Genetic structure and geographic cline analysis revealed that the two lineages of P. guadarramae replace each other abruptly across the sampled region and that gene flow is geographically restricted, implying the existence of strong reproductive isolation. Podarcis bocagei and P. g. lusitanicus show a similar degree of genetic differentiation and reproductive isolation, with very low levels of admixture in syntopy. These results support that all three forms are equally differentiated and reproductively isolated. In consequence, we conclude that the two former subspecies of Podarcis guadarramae constitute valid, yet cryptic species, that should be referred to as P. lusitanicus and P. guadarramae.