Detecting and quantifying introgression in hybridized populations: simplifying assumptions yield overconfidence and uncertainty

Patterns of Performance Variation Between Animal Hybrids and their Parents: A Meta-analysis

Hybridization is a widespread phenomenon in animals, and hybrid heterosis/breakdown could be key processes determining the evolutionary dynamics of hybrids. Indeed, hybrids are not consistently disadvantaged compared to the parental lineages, as was historically assumed. Multiple processes could lead to performance differences between parental lineages and their hybrids. Despite many studies evaluated the performance of hybrids, a quantitative synthesis is required to assess the general pattern. Here we used meta-analytic and meta-regression approaches to quantify the fitness differences between parental lineages and their hybrids, and to identify possible processes that could lead to these differences. Specifically, we tested biological and methodological parameters that could determine differences in performance between hybrids and parental lineages. Hybrid performance was extremely variable across studies, being often significantly higher or lower compared to the mean performance of their parents. Nevertheless, the averaged hybrid performance was similar to the fitness of parental lineages, with differences across studies related to how performance was assessed. Genetic divergence between parental lineages, and the approach used to identify hybrids were the parameters most strongly related to variation in hybrid performance. Performance was lower for hybrids between distantly related lineages. Furthermore, study settings and the use of imprecise approaches for hybrid identification (e.g. morphology-based) can bias assessments of performance. Studies performed on wild populations and using genetic approaches for hybrid identification detected more often a decreased hybrid performance, compared to laboratory studies. We highlight the importance of appropriate settings for a realistic understanding of the evolutionary impacts of hybridization.

Status of the largest extant population of the critically endangered Aeolian lizard Podarcis raffonei (Capo Grosso, Vulcano island)

The Aeolian wall lizard Podarcis raffonei is an island endemic that survives only on three tiny islets, and on the Capo Grosso peninsula of the Vulcano island, thus is among the European vertebrates with the smallest range and one of the most threatened by extinction. This species is declining due to competition and hybridization with the non-native lizard Podarcis siculus, but a regular monitoring program is lacking. Here we assessed the size and status of the Capo Grosso population of P. raffonei on Vulcano. In September 2015 we captured 30 individuals showing the typical brown phenotype of P. raffonei, while one single male showed a green phenotype, apparently intermediate between P. raffonei and the non-native Podarcis siculus. In May 2017, only 47% of 131 individuals showed the typical brown phenotype (P. raffonei-like) and 53% showed the green phenotype (P. siculus-like). Based on N-mixture models and removal sampling the estimated size of the Capo Grosso population was of 800–1300 individuals in 2017, being similar to 2015; available data suggest that the total range of the species could be as small as 2 ha. The frequency of individuals with the typical P. raffonei phenotype dramatically dropped between two samplings with a parallel increase of individuals displaying the green phenotype. Observation on outdoor captive-bred individuals demonstrates plasticity for colouration in P. raffonei individuals from Capo Grosso, with several individuals showing the typical brown pattern in September 2017 and a green pattern in March 2021. Non-exclusive hypotheses, including hybridization with P. siculus and plasticity in colour pattern of P. raffonei, are discussed to explain the phenotypic shifts of the P. raffonei population of Capo Grosso. While genomic evidence is required to reach conclusions and investigate eventual hybridization, it is urgent to undertake a programme for the monitoring and management of this lizard.

Hybridization and rapid differentiation after secondary contact between the native green anole (Anolis carolinensis) and the introduced green anole (Anolis porcatus)

In allopatric species, reproductive isolation evolves through the accumulation of genetic incompatibilities. The degree of divergence required for complete reproductive isolation is highly variable across taxa, which makes the outcome of secondary contact between allopatric species unpredictable. Since before the Pliocene, two species of Anolis lizards, Anolis carolinensis and Anolis porcatus, have been allopatric, yet this period of independent evolution has not led to substantial species-specific morphological differentiation, and therefore, they might not be reproductively isolated. In this study, we determined the genetic consequences of localized, secondary contact between the native green anole, A. carolinensis, and the introduced Cuban green anole, A. porcatus, in South Miami. Using 18 microsatellite markers, we found that the South Miami population formed a genetic cluster distinct from both parental species. Mitochondrial DNA revealed maternal A. porcatus ancestry for 35% of the individuals sampled from this population, indicating a high degree of cytonuclear discordance. Thus, hybridization with A. porcatus, not just population structure within A. carolinensis, may be responsible for the genetic distinctiveness of this population. Using tree-based maximum-likelihood analysis, we found support for a more recent, secondary introduction of A. porcatus to Florida. Evidence that ~33% of the nuclear DNA resulted from a secondary introduction supports the hybrid origin of the green anole population in South Miami. We used multiple lines of evidence and multiple genetic markers to reconstruct otherwise cryptic patterns of species introduction and hybridization. Genetic evidence for a lack of reproductive isolation, as well as morphological similarities between the two species, supports revising the taxonomy of A. carolinensis to include A. porcatus from western Cuba. Future studies should target the current geographic extent of introgression originating from the past injection of genetic material from Cuban green anoles and determine the consequences for the evolutionary trajectory of green anole populations in southern Florida.

Volar plating in distal radius fractures: A prospective clinical study on efficacy of dorsal tangential views to avoid screw penetration

PURPOSE

The purpose of this prospective cohort study of patients treated with volar plating for distal radius fractures is to evaluate the efficacy (defined as detection rate, or the ability to detect dorsally protruding screws) of additional dorsal tangential views (DTV) after obtaining standard anteroposterior (AP) and elevated lateral views by evaluating the change in intraoperative strategy in 100 patients.

MATERIALS AND METHODS

100 patients aged 18 years and older undergoing volar plating for acute extra- or intra- articular distal radius fractures were prospectively enrolled. Intraoperative fluoroscopy views, including AP, elevated lateral and DTV were obtained. Intraoperative -screw- revision frequency for dorsal screw protrusion, screw position relative to volar plate and to dorsal compartment, and screw lengths were evaluated.

RESULTS

Additional DTV led to a change of intraoperative management in 31 of 100 (31%) of patients. A total of 35 out of 504 screws (6.9%) were changed. Screws in the two most radial screws in the plate were at the highest risk of being revised; 16 (46%) screws in most radial position and nine (26%) screws in the 2nd from radial position were revised. Furthermore, five (14%) screws in both the 2nd from ulnar and most ulnar screw holes were revised after DTV. No screws were revised in the central hole. The median length of revised protruding screws was 22 mm (range, 12-26 mm), and these were changed to a mean length of 20  mm (range, 10-22 mm).

CONCLUSION

In this prospective series of 100 patients, obtaining additional DTV is found to be efficacious as it led to change in intraoperative strategy in one-third of patients. We concur with previous pilot studies that DTV, after obtaining conventional AP and elevated lateral views, is advised to avoid dorsally protruding screws, which could minimise the potential for iatrogenic extensor tendon rupture after volar plating for distal radius fractures. Diagnostic accuracy of DTV is subject of a subsequent prospective cohort study with post-operative CT to serve as the reference standard.

LEVEL OF EVIDENCE

.Prognostic I.