Understanding the factors shaping parasite population structure is key to unravelling host-parasite coevolution and transmission dynamics. Respiratory mites of the genus Orthohalarachne (Acari: Halarachnidae) are obligate parasites infecting the respiratory tract of otariids, yet their population genetics remain largely unexplored. Here, we examined the genetic structure of O. attenuata and O. diminuata infecting two sympatric hosts, the South American fur seal (Arctocephalus australis; SAFS) and the South American sea lion (Otaria byronia; SASL), across their distribution ranges. Genetic analyses revealed strong host-associated divergence for both mite species, independent of geographic origin. Variation among host species explained more than 65% of total genetic structure in O. attenuata and more than 57% in O. diminuata, with no haplotypes shared between SAFS- and SASL-associated mites. Despite overlapping distributions and potential interspecific contact, gene flow between mite populations is highly constrained, suggesting prolonged co-divergence with their hosts and limited opportunities for cross-species transmission. Ecological segregation, reproductive timing, and behavioural barriers likely reinforce host specificity. Our findings highlight Orthohalarachne mites as a model system to study parasite diversification and reveal potential cryptic speciation within morphologically indistinguishable lineages. This work underscores the importance of multi-host, spatially wide approaches for understanding the evolutionary and epidemiological dynamics of parasites in marine ecosystems.
The tectonic evolution of a key region in the Andean Patagonian foreland is analysed (42°-43°S). This region exposes the deepest structural level of Patagonia, preserving evidence of large-scale Palaeozoic lithospheric and upper crustal mechanical heterogeneities. The geological record involves multiple extensional and contractional deformation events of the past 200 Myr. Based on new thermochronological data, including apatite fission-track and apatite (U-Th)/He analyses, with surface and subsurface analysis, this research proposes a unified model of tectonic evolution since the onset of the Andean margin. The results reveal a complex interplay of cooling and heating episodes associated with major tectonic phases, including a Late Triassic–Early Jurassic contraction (∼215–200 Ma), Jurassic–Early Cretaceous extension (∼200–143 Ma), two pre-Paleocene contractional phases (∼143–133 Ma and ∼85–62 Ma), a Paleogene extension phase (∼62–20 Ma) and a Miocene contraction event (∼20–10 Ma). Deformation has been largely controlled by Paleozoic metamorphic inheritance and the reactivation of pre-existing structures, regardless of the prevailing tectonic regime. This has led to a lithospheric configuration that alternate between broken foreland systems during contractional events and wide-rift systems during extensional events. This research provides new insights into the long-term geodynamic evolution of intraplate settings in subduction zones with weak lithospheric conditions.
Despite the high abundance of the brittle star Ophiactis asperula in coastal Patagonia, its reproductive biology has not been described. Here, we characterize its reproductive cycle and gametogenic dynamics through a two-year study integrating histological and quantitative reproductive analyses (2010–2012) in the Gulf of San Jorge, Patagonia, Argentina. Of 460 individuals examined (239 males, 201 females, and 20 immature), the sex ratio did not differ from 1:1, and no sexual size dimorphism was detected. Gonadal histology revealed a gonochoric species with multiple oocyte cohorts within ovaries and significant variability in oocyte-size distributions among females. Oocyte diameters ranged from 4 to 96 µm and exhibited marked seasonal variation. Temporal changes in gonadal stages, oocyte-size distribution and the proportion of large oocytes indicated two periods of gametogenic activity: a major pulse extending from austral spring through summer, followed by an extended spawning period during austral summer and early autumn, and a weaker secondary pulse during autumn associated with a minor spawning event in early spring. Maturity indices revealed a broadly synchronous reproductive cycle between sexes, although male maturity generally preceded that of females by one to two months. Reproductive activity was positively associated with seawater temperature and photoperiod, suggesting coupling between gonadal development and seasonal environmental conditions. The relatively small oocytes support a planktotrophic larval strategy, potentially favoring larval release during prolonged periods of enhanced primary productivity. This study provides the first detailed description of O. asperula reproduction, advancing our understanding of reproductive adaptations of echinoderms inhabiting the Magellanic Province.
Arid Patagonia is the southernmost desert in the world and hosts numerous endemic species. However, more than 90% of its surface area is currently affected by desertification, which has prompted the development of restoration practices aimed at mitigating these impacts. In the Lower Chubut River Valley (VIRCH), reduced vegetation cover and increased soil erosion have intensified runoff and sediment transport during rainfall events, leading to sediment discharge into the river and affecting both water supply and agricultural activities. Given that orthopterans are abundant and sensitive to environmental change, this study evaluated the potential of orthopteran assemblages as bioindicators of restoration success in northeastern Patagonia. A subsoiler plowing treatment was implemented to improve environmental conditions and reduce sediment inputs. Using a BACI design with sampling conducted over 4 years (1 year before and 3 years after the intervention), orthopteran assemblages were analysed using multivariate and univariate approaches. Differences in species assemblages between treated and control sites confirmed the effectiveness of the restoration treatment. Treated sites exhibited higher soil moisture and greater vegetation greenness, and orthopterans were more abundant, particularly Miogryllus patagonicus (Cadena-Casta & ntilde;eda, Castelli and Cheli). In contrast, Microgryllus pallipes (Philippi) dominated control sites characterized by senescent vegetation. This study represents the first evidence that orthopteran assemblages can serve as useful bioindicators of restoration processes in South America, highlighting the ecological relevance of orthopteran with epigean habits. Furthermore, our findings provide new tools that may improve conservation and restoration practices in Patagonian ecosystems.
Abstract Understanding how independently evolving lineages arise despite ongoing gene flow remains a central question in evolutionary biology. Although genomic studies increasingly suggest that hybridization can accompany diversification, empirical evidence from ecologically dominant insect groups remains limited. Here, we present the first population-scale phylogenomic analysis of Patagonian ants, sampling Dorymyrmex across approximately 450,000 km 2 . Using genome-wide SNPs, coalescent phylogenetics, phylogenetic networks, demographic modelling, species delimitation, and genome scans, we reconstruct the evolutionary history of this widespread genus. We discovered extensive cryptic diversity with strong genomic differentiation and detected both recent and historical hybridization, demonstrating that substantial genomic divergence accumulated despite recurrent gene flow events. Genome scans further identify candidate loci associated with adaptation to Patagonia’s contrasting environments, suggesting that ecological divergence contributed to lineage diversification. Our results show that cryptic diversification can proceed despite recurrent gene flow, supporting hybridization as an integral component of the diversification process. More broadly, this study illustrates how genome-scale data can reveal hidden biodiversity and the evolutionary processes shaping it in ecologically important but genomically understudied taxa.
