Antarctic Lineages Research Articles

Muted molecular responses to thermal stress in the Antarctic emerald rockcod (Trematomus bernacchii): Proteomic evidence and possible evolutionary mechanisms

The Antarctic emerald rockcod ( Trematomus bernacchii) and its relatives have long been of interest to comparative physiologists, given their history of isolation in extremely cold waters and indications that they lack some or all of the classic “heat shock response.” In this study we complemented previous transcript-level analyses with a comprehensive assessment of the proteomic response to elevated temperatures across three tissues (gill, head kidney, and brain). Animals were exposed to constant conditions at one of three acclimation temperatures, after which a subset were sampled and the remaining individuals experienced an acute heat stress with or without recovery (n=5-6 per treatment). Protein expression patterns were analyzed using tissue-specific, data-independent acquisition (DIA) assay libraries on a UPLC-MS system. The expression patterns reveal a muted response to these different thermal challenges, with only a small number of proteins (out of 2721-3421 per tissue) differentially expressed for any given tissue-treatment combination. The magnitudes of expression changes were also small. These results appear to contradict relatively robust induction patterns for a subset of cellular stress response genes obtained from previous transcriptomic analyses. Furthermore, the differentially expressed proteins were not functionally enriched for any Gene Ontology or KEGG database entries, nor were the promoter regions of the corresponding genetic loci consistently enriched for any transcription factor binding motifs, including those that might be predicted to play a role in the response to hyperthermal stress (such as Hsf1 or HIF). Subsequent bioinformatics approaches within the Perciformes clade suggest modifications to the suite of proteins that regulate translation as a plausible explanation for the lack of a coordinated response to thermal stress in the Antarctic lineage. Overall, our proteomics data offer further detail into the physiological underpinnings of stenothermy in Antarctic fishes. NSF IOS-165582 to WD and an APS John F. Perkins, Jr., Research Career Enhancement Award This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Phylogeographical breaks and limited connectivity among multiple refugia in a pan‐Antarctic moss species

AbstractAimThe historical biogeography of the Antarctic terrestrial flora remains poorly studied and understood. Long‐term in situ persistence of mosses was demonstrated but region‐wide phylogeographical patterns and processes which shaped extant ranges remain largely unknown. Based on a circum‐Antarctic phylogeography, we aim to explore the location of glacial refugia, especially the possibility of their existence in the continent, patterns of possible connections between extant discrete populations, local colonisation routes and barriers to gene flow, hence relative importance of connectivity and isolation.LocationAntarctica, South America, Australia and New Zealand.TaxonSyntrichia sarconeurum Ochyra & R.H.Zander (Pottiaceae).MethodsWe used a range‐wide, taxonomically informed sampling and multilocus sequencing of nuclear and chloroplast DNA regions. The temporal evolutionary framework, spatial genetic structure and regional diversification were assessed using phylogenetic reconstruction (maximum likelihood and Bayesian inference), molecular dating, phylogeographical analyses and reconstruction of ancestral areas.ResultsWe found a striking genetic structure of the Antarctic Syntrichia sarconeurum populations that deviates from previous reports on mosses. The presence of two allopatric cpDNA haplotypes indicated a long‐term isolation of the continental populations. Nuclear ITS revealed three major lineages with a main genetic break largely consistent with plastid data. Significant phylogeographical structure was further supported by NST/FST comparison, raggedness index and mismatch analyses. Diversification of the Antarctic lineages occurred within the Pleistocene, since about 1.36 Ma.Main ConclusionsThe genetic break genetic break revealed in the phylogeographical structure coincides with the Gressit line, a biogeographical separation area between the biota of the Antarctic Peninsula and the main continental Antarctica. It indicates limited connectivity of populations and suggests that S. sarconeurum has survived in multiple refugia both in the peripheral areas of the Antarctic and within the continent over several glacial periods. Differences in genetic diversity observed between these areas may hypothetically reflect asymmetric changes in reproductive mode in the past.

An ancient, Antarctic-specific species complex: large divergences between multiple Antarctic lineages of the tardigrade genus Mesobiotus

Antarctica has been isolated and progressively glaciated for over 30 million years, with only approximately 0.3 % of its area currently ice-free and capable of supporting terrestrial ecosystems. As a result, invertebrate populations have become isolated and fragmented, in some cases leading to speciation. Terrestrial invertebrate species currently found in Antarctica often show multi-million year, and even Gondwanan, heritage, with little evidence of recent colonisation. Mesobiotus is a globally distributed tardigrade genus. It has commonly been divided into two “groups”, referred to as harmsworthi and furciger, with both groups currently considered cosmopolitan, with global reports including from both the Arctic and the Antarctic. However, some authors considered that Meb. furciger, as originally described, may represent an Antarctic-specific lineage. Using collections of tardigrades from across the Antarctic continent and publicly available sequences obtained from online databases, we use mitochondrial and nuclear ribosomal sequence data to clarify the relationships of Antarctic Mesobiotus species. Our analyses show that all Antarctic members belong to a single lineage, evolving separately from non-Antarctic representatives. Within this Antarctic lineage there are further deep divisions among geographic regions of the continent, consistent with the presence of a species complex. Based on our data confirming the deep divisions between this Antarctic lineage, which includes representatives of both groups, we recommend that the use of furciger and harmsworthi group terminology is now abandoned, as it leads to systematic and biogeographical confusion.

Cenozoic climatic changes drive evolution and dispersal of coastal benthic foraminifera in the Southern Ocean

The Antarctic coastal fauna is characterized by high endemism related to the progressive cooling of Antarctic waters and their isolation by the Antarctic Circumpolar Current. The origin of the Antarctic coastal fauna could involve either colonization from adjoining deep-sea areas or migration through the Drake Passage from sub-Antarctic areas. Here, we tested these hypotheses by comparing the morphology and genetics of benthic foraminifera collected from Antarctica, sub-Antarctic coastal settings in South Georgia, the Falkland Islands and Patagonian fjords. We analyzed four genera (Cassidulina, Globocassidulina, Cassidulinoides, Ehrenbergina) of the family Cassidulinidae that are represented by at least nine species in our samples. Focusing on the genera Globocassidulina and Cassidulinoides, our results showed that the first split between sub-Antarctic and Antarctic lineages took place during the mid-Miocene climate reorganization, probably about 20 to 17 million years ago (Ma). It was followed by a divergence between Antarctic species ~ 10 Ma, probably related to the cooling of deep water and vertical structuring of the water-column, as well as broadening and deepening of the continental shelf. The gene flow across the Drake Passage, as well as between South America and South Georgia, seems to have occurred from the Late Miocene to the Early Pliocene. It appears that climate warming during 7–5 Ma and the migration of the Polar Front breached biogeographic barriers and facilitated inter-species hybridization. The latest radiation coincided with glacial intensification (~ 2 Ma), which accelerated geographic fragmentation of populations, demographic changes, and genetic diversification in Antarctic species. Our results show that the evolution of Antarctic and sub-Antarctic coastal benthic foraminifera was linked to the tectonic and climatic history of the area, but their evolutionary response was not uniform and reflected species-specific ecological adaptations that influenced the dispersal patterns and biogeography of each species in different ways.

Accelerated evolution at chaperone promoters among Antarctic notothenioid fishes

BackgroundAntarctic fishes of the Notothenioidei suborder constitutively upregulate multiple inducible chaperones, a highly derived adaptation that preserves proteostasis in extreme cold, and represent a system for studying the evolution of gene frontloading. We screened for Hsf1-binding sites, as Hsf1 is a master transcription factor of the heat shock response, and highly-conserved non-coding elements within proximal promoters of chaperone genes across 10 Antarctic notothens, 2 subpolar notothens, and 17 perciform fishes. We employed phylogenetic models of molecular evolution to determine whether (i) changes in motifs associated with Hsf1-binding and/or (ii) relaxed purifying selection or exaptation at ancestral cis-regulatory elements coincided with the evolution of chaperone frontloading in Antarctic notothens.ResultsAntarctic notothens exhibited significantly fewer Hsf1-binding sites per bp at chaperone promoters than subpolar notothens and Serranoidei, the most closely-related suborder to Notothenioidei included in this study. 90% of chaperone promoters exhibited accelerated substitution rates among Antarctic notothens relative to other perciformes. The proportion of bases undergoing accelerated evolution (i) was significantly greater in Antarctic notothens than in subpolar notothens and Perciformes in 70% of chaperone genes and (ii) increased among bases that were more conserved among perciformes. Lastly, we detected evidence of relaxed purifying selection and exaptation acting on ancestrally conserved cis-regulatory elements in the Antarctic notothen lineage and its major branches.ConclusionA large degree of turnover has occurred in Notothenioidei at chaperone promoter regions that are conserved among perciform fishes following adaptation to the cooling of the Southern Ocean. Additionally, derived reductions in Hsf1-binding site frequency suggest cis-regulatory modifications to the classical heat shock response. Of note, turnover events within chaperone promoters were less frequent in the ancestral node of Antarctic notothens relative to younger Antarctic lineages. This suggests that cis-regulatory divergence at chaperone promoters may be greater between Antarctic notothen lineages than between subpolar and Antarctic clades. These findings demonstrate that strong selective forces have acted upon cis-regulatory elements of chaperone genes among Antarctic notothens.

Genetic and morphological variations of the lichenized fungus Steinera intricata (Arctomiaceae, Lecanoromycetes) from southern South America to Antarctic Peninsula

Steinera (Arctomiaceae, Lecanoromycetes) is an Austral genus of lichenized fungi that form symbiotic associations with cyanobacteria, producing small and inconspicuous thalli. Most species of Steinera present a high degree of endemism restricted to sub-Antarctic islands except S. intricata which occurs from southern South America to the Antarctic Peninsula and presents remarkable phenotypic variation along its distribution range. In this study, an integrative approach was used to explore the extent of intraspecific diversity of S. intricata throughout its distribution. Morphological and anatomical descriptions and the phylogenetic analyses of three genomic regions were performed with specimens collected from seven Antarctic islands and in the Tierra del Fuego National Park (Argentina). Genetic data revealed species-level lineages are not associated with the differences observed in the thalli shape, which probably are related to distinct microhabitats and substrates as well as to the development stage. Molecular clock analyses estimated that S. intricata originated at about 0.24 Myr and that the diversification of the Antarctic lineages occurred at about 0.16 Myr. This study revealed that there is probably an unknown diversity of new members of Steinera in southern South America and that the evolutionary history of these cyanolichens may contribute to the understanding of the phylogeographic connections between members of the Austral-Antarctic flora.

An amended description of two Gyrodactylus species (Platyhelminthes: Monogenea) parasitizing Antarctic Notothenioid fish.

Species identification based on the morphometry of opisthaptoral hard parts, in combination with internal transcribed spacer ribosomal DNA (ITS rDNA) region sequences, confirmed the presence of four viviparous Gyrodactylus von Nordman, 1832 (Plathyhelminthes, Monogenea) species on Nototheniid fish from the Prince Gustav Channel (Weddell Sea, Antarctica). Gyrodactylus antarcticus Gusev, 1967 was found mostly on Trematomus newnesi Boulenger (93 specimens) but also on T. bernacchii Boulenger (one specimen), the latter representing a new host record for this species. Gyrodactylus byrdi Hargis & Dillon, 1968 and G. coriicepsi Rokicka, Lumme & Ziętara, 2009 were recorded on their type hosts, T. newnesi and Notothenia coriiceps Richardson, respectively. Gyrodactylus wilkesi Hargis & Dillon, 1968 was found mostly on the fins of T. bernacchii (29 specimens), but also on T. hansoni Boulenger (one specimen) and T. newnesi (three specimens). The finding of G. wilkesi on T. newnesi represents a new host record. The low number of Gyrodactylus specimens may indicate an accidental infection. The occurence of all four Gyrodactylus species in the Prince Gustav Channel represents a new locality record. According to phylogentic methods, the newly redescribed monogeneans belong to the Antarctic lineage, forming a sister group to North American and European marine Gyrodactylus species, and consist of two species groups, one comprising G. coriicepsi and G. nudifronsi Rokicka, Lumme & Ziętara, 2009, and the other G. anarcticus and G. wilkesi.

An Antarctic flock under the Thorson's rule: Diversity and larval development of Antarctic Velutinidae (Mollusca: Gastropoda)

In most marine gastropods, the duration of the larval phase is a key feature, strongly influencing species distribution and persistence. Antarctic lineages, in agreement with Thorson's rule, generally show a short pelagic developmental phase (or lack it completely), with very few exceptions. Among them is the ascidian-feeding gastropod family Velutinidae, a quite understudied group. Based on a multilocus (COI, 16S, 28S and ITS2) dataset for 182 specimens collected in Antarctica and other regions worldwide, we investigated the actual Antarctic velutinid diversity, inferred their larval development, tested species genetic connectivity and produced a first phylogenetic framework of the family. We identified 15 Antarctic Molecular Operational Taxonomic Units (MOTUs), some of which represented undescribed species, which show two different types of larval shell, indicating different duration of the Pelagic Larval Phase (PLD). Antarctic velutinids stand as an independent lineage, sister to the rest of the family, with extensive hidden diversity likely produced by rapid radiation. Our phylogenetic framework indicates that this Antarctic flock underwent repeated events of pelagic phase shortening, in agreement with Thorson's rule, yielding species with restricted geographic ranges.

Evolution in chronic cold: varied loss of cellular response to heat in Antarctic notothenioid fish

BackgroundConfined within the freezing Southern Ocean, the Antarctic notothenioids have evolved to become both cold adapted and cold specialized. A marked signature of cold specialization is an apparent loss of the cellular heat shock response (HSR). As the HSR has been examined in very few notothenioid species to-date, it remains unknown whether HSR loss pervades the Antarctic radiation, or whether the broader cellular responses to heat stress has sustained similar loss. Understanding the evolutionary status of these responses in this stenothermal taxon is crucial for evaluating its adaptive potential to ocean warming under climate change.ResultsIn this study, we used an acute heat stress protocol followed by RNA-Seq analyses to study the evolution of cellular-wide transcriptional responses to heat stress across three select notothenioid lineages - the basal temperate and nearest non-Antarctic sister species Eleginops maclovinus serving as ancestral proxy, the cryopelagic Pagothenia borchgrevinki and the icefish Chionodraco rastrospinosus representing cold-adapted red-blooded and hemoglobinless Antarctic notothenioids respectively. E. maclovinus displayed robust cellular stress responses including the ER Unfolded Protein Response and the cytosolic HSR, cementing the HSR as a plesiomorphy that preceded Antarctic notothenioid radiation. While the transcriptional response to heat stress was minimal in P. borchgrevinki, C. rastrospinosus exhibited robust responses in the broader cellular networks especially in inflammatory responses despite lacking the classic HSR and UPR.ConclusionThe disparate patterns observed in these two archetypal Antarctic species indicate the evolutionary status in cellular ability to mitigate acute heat stress varies even among Antarctic lineages, which may affect their adaptive potential in coping with a warming world.

Locked in the icehouse: Evolution of an endemic Epimeria (Amphipoda, Crustacea) species flock on the Antarctic shelf

The Antarctic shelf’s marine biodiversity has been greatly influenced by the climatic and glacial history of the region. Extreme temperature changes led to the extinction of some lineages, while others adapted and flourished. The amphipod genus Epimeria is an example of the latter, being particularly diverse in the Antarctic region. By reconstructing a time-calibrated phylogeny based on mitochondrial (COI) and nuclear (28S and H3) markers and including Epimeria species from all oceans, this study provides a temporal and geographical framework for the evolution of Antarctic Epimeria. The monophyly of this genus is not supported by Bayesian Inference, as Antarctic and non-Antarctic Epimeria form two distinct well-supported clades, with Antarctic Epimeria being a sister clade to two stilipedid species. The monophyly of Antarctic Epimeria suggests that this clade evolved in isolation since its origin. While the precise timing of this origin remains unclear, it is inferred that the Antarctic lineage arose from a late Gondwanan ancestor and hence did not colonize the Antarctic region after the continent broke apart from the other fragments of Gondwanaland. The initial diversification of the clade occurred 38.04Ma (95% HPD [48.46Ma; 28.36Ma]) in a cooling environment. Adaptation to cold waters, along with the extinction of cold-intolerant taxa and resulting ecological opportunities, likely led to the successful diversification of Epimeria on the Antarctic shelf. However, there was neither evidence of a rapid lineage diversification early in the clade’s history, nor of any shifts in diversification rates induced by glacial cycles. This suggests that a high turnover rate on the repeatedly scoured Antarctic shelf could have masked potential signals of diversification bursts.

Morphological and genetic data clarify the taxonomic status of Colossendeis robusta and C. glacialis (Pycnogonida) and reveal overlooked diversity

Colossendeis robusta Hoek, 1881, originally described from the Kerguelen shelf, is considered as one of the most widespread Antarctic pycnogonids. However, the taxonomic status of this and similar species has long been unclear, as synonymy of C. glacialis Hodgson, 1907 and several other species with C. robusta has been proposed. Here we test the synonymy of C. robusta and C. glacialis with two independent molecular markers as well as comprehensive morphometric measurements and SEM data of the ovigeral spine configuration. We show that C. robusta and C. glacialis are clearly distinct species, and our results also indicate the existence of another previously unrecognized Antarctic species, C. bouvetensis sp.n., as well as an Antarctic lineage closely related to the endemic Kerguelen group C. robusta s.str. We find evidence for strong regional differentiation within each species. Our results suggest that diversity of Antarctic pycnogonids is still underestimated.

Spatial genetic heterogeneity of the cosmopolitan chaetognath Eukrohnia hamata (Möbius, 1875) revealed by mitochondrial DNA

Some holoplanktonic species are cosmopolitan and have continuous distribution in the world’s oceans. For most of these species it is not clear whether there is unhampered gene flow between far distant populations or they represent a complex of cryptic species. In the present study we investigated genetic diversity of the cosmopolitan chaetognath Eukrohnia hamata in order to identify its spatial structure. DNA-barcode fragment of the mitochondrial COI gene was determined and analyzed for E. hamata specimens collected in the Arctic Ocean, Atlantic Ocean, and Atlantic sector of the Southern Ocean. Five lineages were determined by the phylogenetic analysis with robust statistical support. Three lineages: Antarctic (Eh-1), Subantarctic (Eh-2), and Arctic (Eh-3) had significant genetic differences and were geographically separated. Two other lineages: Eh-4 and Eh-5, that had the smallest genetic difference, were observed together in tropical waters, but they were geographically separated from the other lineages. We suppose that geographical distribution of most of the E. hamata lineages is shaped by the large-scale oceanic fronts, considered as biogeographic boundaries for numerous zooplankton species. Genetic homogeneity of Arctic, Subantarctic, and Antarctic lineages was also shown, each within its regions of inhabit.

Molecular Evidence for Distinct Antarctic Lineages in the Cosmopolitan Terrestrial Diatoms Pinnularia borealis and Hantzschia amphioxys

Recent morphology-based studies indicate that freshwater diatom floras in the Antarctic comprise a significant share of endemics among a majority of apparently cosmopolitan species. Given the widespread (pseudo)cryptic species diversity in diatoms, we assessed the molecular divergence and temperature-dependent growth characteristics between Antarctic and non-Antarctic strains for two presumed species with a cosmopolitan distribution, namely Pinnularia borealis and Hantzschia amphioxys. Molecular phylogenies based on the plastid gene rbcL and the nuclear 28S rDNA (D1-D3 region) revealed that both taxa consist of multiple lineages, each including a distinct Antarctic lineage. A molecular clock estimates the origin of P. borealis at 35.8 (30-47) million years (Ma) ago, making this the oldest known diatom species complex. The Antarctic P. borealis lineage is estimated to have diverged 7.8 (2-15) Ma ago, after the geographical and thermal isolation of the Antarctic continent. Despite not being psychrophilic, the Antarctic lineages of P. borealis and H. amphioxys have a lower optimal growth temperature and upper lethal temperature than most lineages from more temperate regions, indicating niche differentiation. Together, this suggests that many presumed cosmopolitan Antarctic diatom species are in fact species complexes, possibly containing Antarctic endemics with low temperature preferences.

Mitochondrial function in Antarctic nototheniids with ND6 translocation.

Fish of the suborder Notothenioidei have successfully radiated into the Southern Ocean and today comprise the dominant fish sub-order in Antarctic waters in terms of biomass and species abundance. During evolution in the cold and stable Antarctic climate, the Antarctic lineage of notothenioids developed several unique physiological adaptations, which make them extremely vulnerable to the rapid warming of Antarctic waters currently observed. Only recently, a further phenomenon exclusive to notothenioid fish was reported: the translocation of the mitochondrial gene encoding the NADH Dehydrogenase subunit 6 (ND6), an indispensable part of complex I in the mitochondrial electron transport system.This study investigated the potential physiological consequences of ND6 translocation for the function and thermal sensitivity of the electron transport system in isolated liver mitochondria of the two nototheniid species Notothenia coriiceps and Notothenia rossii, with special attention to the contributions of complex I (NADH DH) and complex II (Succinate DH) to oxidative phosphorylation. Furthermore, enzymatic activities of NADH∶Cytochrome c Oxidoreductase and Cytochrome C Oxidase were measured in membrane-enriched tissue extracts.During acute thermal challenge (0–15°C), capacities of mitochondrial respiration and enzymatic function in the liver could only be increased until 9°C. Mitochondrial complex I (NADH Dehydrogenase) was fully functional but displayed a higher thermal sensitivity than the other complexes of the electron transport system, which may specifically result from its unique amino acid composition, revealing a lower degree of stability in notothenioids in general. We interpret the translocation of ND6 as functionally neutral but the change in amino acid sequence as adaptive and supportive of cold stenothermy in Antarctic nototheniids. From these findings, an enhanced sensitivity to ocean warming can be deduced for Antarctic notothenioid fish.

Molecular Species Identification of Astrotoma agassizii from Planktonic Embryos: Further Evidence for a Cryptic Species Complex

The phrynophiurid brittle star Astrotoma agassizii is abundant in the cold temperate Magellanic region of South America and has a circumpolar Antarctic distribution. Three genetically distinct lineages were recently identified, with one in Antarctica geographically and genetically isolated from both South American lineages (Hunter R, Halanych KM. 2008. Evaluating connectivity in the brooding brittle star Astrotoma agassizii across the Drake Passage in the Southern Ocean. J Hered. 99:137-148.). Despite being an apparent brooding species, A. agassizii displayed a high genetic homogeneity at 2 mitochondrial markers (16s and COII) across a geographical range of more than 500 km along the Antarctic Peninsula. Here, using 16s ribosomal RNA sequences, we match a variety of early developmental stages (fertilized eggs, embryos; n = 12) collected from plankton samples in the Ross Sea to sequences of A. agassizii from the Antarctic Peninsula. The single 16s haplotype reported here is an identical match to one 16s haplotype found for A. agassizii from the Antarctic Peninsula, more than 5000 km away. Based on the regular occurrence of A. agassizii developmental stages in plankton samples, we propose that the Antarctic lineage of this species has a planktonic dispersive stage, with brooding restricted to the South American lineages. A different developmental mode would provide further evidence for cryptic speciation in this brittle star.

Hidden levels of phylodiversity in Antarctic green algae: further evidence for the existence of glacial refugia

Recent data revealed that metazoans such as mites and springtails have persisted in Antarctica throughout several glacial-interglacial cycles, which contradicts the existing paradigm that terrestrial life was wiped out by successive glacial events and that the current inhabitants are recent colonizers. We used molecular phylogenetic techniques to study Antarctic microchlorophyte strains isolated from lacustrine habitats from maritime and continental Antarctica. The 14 distinct chlorophycean and trebouxiophycean lineages observed point to a wide phylogenetic diversity of apparently endemic Antarctic lineages at different taxonomic levels. This supports the hypothesis that long-term survival took place in glacial refugia, resulting in a specific Antarctic flora. The majority of the lineages have estimated ages between 17 and 84 Ma and probably diverged from their closest relatives around the time of the opening of Drake Passage (30-45 Ma), while some lineages with longer branch lengths have estimated ages that precede the break-up of Gondwana. The variation in branch length and estimated age points to several independent but rare colonization events.

Palynological record of the Paleogene Río Leona Formation (southernmost South America): Stratigraphical and paleoenvironmental implications

Terrestrial palynomorph assemblages have been recovered from the Río Leona Formation, southwestern Santa Cruz Province, southern South America. Organic debris (spores, pollen grains, fresh water algae, plant tissues and fungi) are preserved in shales associated with other plant fossil remains (leaves and wood). The Río Leona Formation is here assigned to the early Late Oligocene based on the presence of key species of the M–M palynological zone ( Margocolporites tenuireticulatus Barreda, Diporites aspis Pocknall and Mildenhall, Granodiporites nebulosus Partridge, Mutisiapollis spp.) and the virtual absence of warmth-adapted taxa (abundant from the latest Late Oligocene to Middle Miocene in Patagonia). A temporal gap between the Río Leona Formation and the overlying Centinela Formation (Early Miocene) – exposed in the studied region – is suggested here based on the differences observed in their palynological assemblages. The Río Leona Formation was deposited in a continental environment, with local peat swamps and coastal plain environments. The presence of Antarctic lineages in the lower and middle sections of the Río Leona Formation is consistent with the cooling trend globally recognized during the Late Eocene and Early Oligocene times. The appearance of some Neotropical families in the upper section might indicate the beginning of the Late Oligocene warming event. Records of Asteraceae ( Mutisiapollis telleriae Barreda and Palazzesi sp. nov.), Menyanthaceae ( Striasyncolpites laxus Mildenhall and Pocknall), and Rosaceae ( Psilatricolporites quenua Barreda and Palazzesi sp. nov., Psilatricolporites sp.) are the oldest reports in Patagonia to date, and provide significant information on the early divergence and radiation times of these major angiosperm families.

Fossil weevils (Coleoptera: Curculionidae) from latitude 85°S Antarctica

Two species of fossil listroderine weevils (Coleoptera: Curculionidae: Rhytirhinini: Listroderina) are reported from the Meyer Desert Formation at a locality on the Beardmore Glacier in the Transantarctic Mountains about 500 km from the South Pole. Associated fossils include wood, leaves and pollen of Nothofagus, stems and leaves of several species of mosses, achenes of Ranunculus, shells of freshwater molluscs and a fish tooth. The age of the fossiliferous strata is contentious but probably within the range of Pliocene to mid-Miocene. The fossils represent organisms that colonised the margins of a glacier at the head of a fjord during an interglaciation. The autecology of the listroderine species indicates that temperatures during summer months averaged 5°C. The mean annual temperature, with winter temperatures constrained by 6 months of darkness, is estimated to have been about −8°C compared to the −26°C estimated for sea level at latitude 85°S today. The closest evolutionary link of the fossil listroderines is with South American rather than Australian or New Zealand taxa. Divergence of the taxa, at least at the level of tribe, had most probably occurred on Gondwana before the continent broke apart. The fossil species are considered to be the descendants of Antarctic lineages which evolved on the continent in the Late Cretaceous or Palaeogene and survived until the Neogene. Extinction of the listroderines and most other Antarctic terrestrial biota occurred with the growth of the polar ice sheets and the change to the polar desert climate.

Charadriiform Birds in Antarctica: Behavioral, Morphological, and Physiological Adjustments Conserving Reproductive Success

Birds colonizing different climates must alter some aspect of their breeding biology to maintain successful reproduction. Comparative analyses were used to elucidate the changes in parental behavior and in the rate of development of the young associated with successful breeding of charadriiform birds in Antarctica. The species studied, the kelp gull Larus dominicanus, the South Polar skua Catharacta maccormicki, and the greater sheathbill Chionis alba, represent three of the four independent colonizations of Antarctica by charadriiform birds. Antarctic species brooded their young two to five times longer than did their temperate relatives. The Antarctic young had greater tolerance to hypothermia, which suggests that, historically, parental care failed to protect the young from selection by low temperatures. Antarctic hatchlings were neither larger nor metabolically more mature than their relatives. Despite presumed selection on the young by low temperatures and the presence of individual variation in development, the young did not attain homeothermy significantly earlier than did their temperate relatives. Growth rates over the entire nestling period were also similar for Antarctic and temperate species. The Antarctic young did grow faster to a moderate size more favorable for thermoregulation and showed coordinately faster development of resting metabolic rate. South Polar skuas, from the oldest Antarctic lineage, further diverged in having accelerated development of thermogenesis, which substantially reduced their reliance on parental brooding. Evolutionary changes in physiological development of the young have resulted in improved abilities to tolerate hypothermia and in lower costs, relative to peak metabolic rates, to maintain homeothermy.