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Phylogenetic relationships of the North American catfishes (Ictaluridae, Siluriformes): Investigating the origins and parallel evolution of the troglobitic species
Abstract
Insular habitats have played an important role in developing evolutionary theory, including natural selection and island biogeography. Caves are insular habitats that place extreme selective pressures on organisms due to the absence of light and food scarcity. Therefore, cave organisms present an excellent opportunity for studying colonization and speciation in response to the unique abiotic conditions that require extreme adaptations. One vertebrate family, the North American catfishes (Ictaluridae), includes four troglodytic species that inhabit the karst region bordering the western Gulf of Mexico. The phylogenetic relationships of these species have been contentious, and conflicting hypotheses have been proposed to explain their origins. The purpose of our study was to construct a time-calibrated phylogeny of Ictaluridae using first-occurrence fossil data and the largest molecular dataset on the group to date. We test the hypothesis that troglodytic ictalurids have evolved in parallel, thus resulting from repeated cave colonization events. We found that Prietella lundbergi is sister to surface-dwelling Ictalurus and that Prietella phreatophila + Trogloglanis pattersoni are sister to surface-dwelling Ameiurus, suggesting that ictalurids colonized subterranean habitats at least twice in evolutionary history. The sister relationship between Prietella phreatophila and Trogloglanis pattersoni may indicate that these two species diverged from a common ancestor following a subterranean dispersal event between Texas and Coahuila aquifers. We recovered Prietella as a polyphyletic genus and recommend P. lundbergi be removed from this genus. With respect to Ameiurus, we found evidence for a potentially undescribed species sister to A. platycephalus, which warrants further investigation of Atlantic and Gulf slope Ameiurus species. In Ictalurus, we identified shallow divergence between I. dugesii and I. ochoterenai, I. australis and I. mexicanus, and I. furcatus and I. meridionalis, indicating a need to reexamine the validity of each species. Lastly, we propose minor revisions to the intrageneric classification of Noturus including the restriction of subgenus Schilbeodes to N. gyrinus (type species), N. lachneri, N. leptacanthus, and N. nocturnus.
... To make the tree and our dataset compatible for analysis, we used the mean shape of the two samples of each species and trimmed the phylogenetic tree to include only our sampled taxa using Mesquite (Version 3.81, build 955). All sampled species were monophyletic, which allowed us to collapse the multiple clades of each species of Janzen et al. (2023) into a single tip ( Figure 2). We also tested phylogenetic signal Κ mult using the Physignal function from the geomorph package on the trimmed tree and mean shape of each species (Adams, 2014). ...
The Weberian apparatus is a hearing specialization unique to the otophysan fishes, and an unexpected degree of morphological variation exists in species of the Noturus catfishes. Our aim in this study is to investigate relationships between morphological variations and ecology that may drive this variation. Sampling 48 specimens representing 25 species, we investigated morphological diversity and accounted for ecological variables using landmark‐based 3D geometric morphometrics and x‐ray‐based computed tomography (CT) images. We tested five ecological variables using three landmark sets in three focused regions: the tripus, scaphium, and overall shape of the peripheral structures including the complex vertebra. We performed phylogenetic signal tests, and phylogenetic influence is not significant within Noturus in any of the three regions. Among the tested ecological variables, stream velocity and coloration (a proxy for substrate) were found to be significantly associated with the morphology of the tripus and scaphium, the first and the last ossicles of the sound transmitting chain. This eco‐morphology connection may be mediated through stream velocity's dominant role in defining the soundscape of aquatic environments and substrate material properties contributing to which sounds are produced and propagated. We conclude that Noturus catfishes could be acoustically adapted to their microhabitats.
Hybridization, defined as the crossing between individuals from different populations, is a common phenomenon in fishes. Moreover, many fish hybrids have been developed to be used in aquaculture. Among these, catfish order Siluriformes is one of the most numerous groups of fishes, with some interspecific natural and anthropogenic crosses reported. We conducted a systematic review of studies on catfish hybridization published up until 2023, recovering 158 relevant papers with 80 crosses reported. More than 90% of these studies referred to anthropogenic hybridization, mostly reporting hybrids used in aquaculture, and only 8% referred to natural hybridization. The capacity for interspecific hybridization within catfish is demonstrated, with reports of crosses even among highly divergent species, suggesting potential alloploidization changes and epigenetic mechanisms facilitating such crosses. Nonetheless, further exploration using genomic approaches is needed to prove these hypotheses. Morphology was the most common method of catfish hybrid inference (26.6%), followed by mitochondrial DNA markers (16.3%), karyology (10.9%), and other DNA- and protein-based methods. Despite the large amount of research, a lack of genomic studies is highlighted here, with only one paper using genomics for hybrid inference. We highlight that the use of genomics can help to disentangle evolutionary history of catfish hybridization and to understand the negative impact of anthropogenic hybridization over threatened catfish species. The use of genomic tools will help to provide deeper insights into catfish hybridization, thereby informing conservation efforts and sustainable aquaculture practices.
Graphical abstract
Background
Ictalurus is one of the most representative groups of North American freshwater fishes. Although this group has a well-studied fossil record and has been the subject of several morphological and molecular phylogenetic studies, incomplete taxonomic sampling and insufficient taxonomic studies have produced a rather complex classification, along with intricate patterns of evolutionary history in the genus that are considered unresolved and remain under debate.
Results
Based on four loci and the most comprehensive taxonomic sampling analyzed to date, including currently recognized species, previously synonymized species, undescribed taxa, and poorly studied populations, this study produced a resolved phylogenetic framework that provided plausible species delimitation and an evolutionary time framework for the genus Ictalurus .
Conclusions
Our phylogenetic hypothesis revealed that Ictalurus comprises at least 13 evolutionary units, partially corroborating the current classification and identifying populations that emerge as putative undescribed taxa. The divergence times of the species indicate that the diversification of Ictalurus dates to the early Oligocene, confirming its status as one of the oldest genera within the family Ictaluridae.
Background
Ictalurus is one of the most representative groups of North American freshwater fishes. Although this group has a well-studied fossil record, and has been the subject of several morphological and molecular phylogenetic studies, incomplete taxonomic sampling and insufficient taxonomic studies have produced a rather complex classification along with intricate evolutionary history patterns of the genus that are considered unresolved and remain under debate.
Results
Based on four loci and the most comprehensive taxonomic sampling analyzed to date, including currently recognized species, previously synonymized species, undescribed taxa, as well as poorly studied populations, this study produced a resolved phylogenetic framework that provided plausible species delimitation and an evolutionary time framework for the genus Ictalurus in North America.
Conclusions
Our phylogenetic hypothesis revealed that Ictalurus comprises at least 13 evolutionary units, partially corroborating the current classification and identifying populations that emerge as putative undescribed taxa. The divergence times of the species indicate that diversification of Ictalurus dates back to the early Oligocene, confirming its status as one of the oldest genera within the family Ictaluridae.
Several hundred catfish species (order: Siluriformes) belonging to 11 families inhabit Africa, of which at least six families are endemic to the continent. Although four of those families are well‐known to belong to the ‘Big‐Africa clade’, no previous study has addressed the phylogenetic placement of the endemic African catfish family Austroglanididae in a comprehensive framework with molecular data. Furthermore, interrelationships within the ‘Big‐Africa clade’, including the most diverse family Mochokidae, remain unclear. This study was therefore designed to help reconstruct inter‐ and intrarelationships of all currently valid mochokid genera, to infer their position within the ‘Big Africa clade’ and to establish a first molecular phylogenetic hypothesis of the relationships of the enigmatic Austroglanididae within the Siluriformes. We assembled a comprehensive mitogenomic dataset comprising all protein coding genes and representing almost all recognized catfish families (N = 33 of 39) with carefully selected species (N = 239). We recovered the monophyly of the previously identified multifamily clades ‘Big Asia’ and ‘Big Africa’ and determined Austroglanididae to be closely related to Pangasiidae, Ictaluroidea and Ariidae. Mochokidae was recovered as the sister group to a clade encompassing Auchenoglanididae, Claroteidae, Malapteruridae and the African Schilbeidae, albeit with low statistical support. The two mochokid subfamilies Mochokinae and Chiloglanidinae as well as the chiloglanid tribe Atopochilini were recovered as reciprocally monophyletic. The genus Acanthocleithron forms the sister group of all remaining Mochokinae, although with low support. The genus Atopodontus is the sister group of all remaining Atopochilini. In contrast to morphological reconstructions, the monophyly of the genus Chiloglanis was strongly supported in our analysis, with Chiloglanis macropterus nested within a Chiloglanis sublineage encompassing only other taxa from the Congo drainage. This is an important result because the phylogenetic relationships of C. macropterus have been controversial in the past, and because we and other researchers assumed that this species would be resolved as sister to most or all other members of Chiloglanis. The apparent paraphyly of Synodontis with respect to Microsynodontis provided an additional surprise, with Synodontis punu turning out to be the sister group of the latter genus.
The Edwards aquifer system is one of the great karstic aquifer systems of the world. It supplies water for more than 2 million people and for agricultural, municipal, industrial, and recreational uses. The Edwards (Balcones Fault Zone) Aquifer in the San Antonio, Texas, area was the first to be designated a sole source aquifer by the Environmental Protection Agency in 1975. The Edwards Aquifer also hosts unique groundwater, cave, and spring ecosystems. This 27-chapter memoir reviews the current state of knowledge, current and emerging challenges to wise use of the aquifer system, and some of the technologies that must be adopted to address these challenges.
Subterranean environments are poorly known regarding many ecological aspects, such as community structure and its response to different disturbances. To estimate the effects of ground area lost in a limestone cave community in Southeastern Brazil, the invertebrate fauna was sampled before 76% of the cave floor was submerged by the filling of a hydroeletric power plant reservoir. Then, a 2-year monitoring was conducted. A species-area curve based on empiric data was constructed and the z-value of the species-area equation was calculated, what allowed estimating the expected cave richness after flooding comparing with data obtained during the monitoring. The results support the species-area relationship hypothesis; the cave community showed a drastic reduction of richness after losing area. Furthermore, it was also possible to estimate the species richness using the species-area equation. Moreover, the cave community showed a high temporal beta diversity when comparing the community sampled before and after the inundation; this pattern becomed less pronunciated over time. A high z-value (z = 0.58) was found for the cave species-area equation, indicating that subterranean communities are even more damaged by area loss than other environments probably due to the reduced mobility of cave invertebrates and the physical isolation of this environment. The present study highlighted that area loss resulted in a drastic reduction of cave richness. Additionally, it became evident that whenever possible studies should consider the original condition of a cave community and their responses after disturbances. Such strategy is critically important for conservation purposes.
Elaboration of Bayesian phylogenetic inference methods has continued at pace in recent years with major new advances in nearly all aspects of the joint modelling of evolutionary data. It is increasingly appreciated that some evolutionary questions can only be adequately answered by combining evidence from multiple independent sources of data, including genome sequences, sampling dates, phenotypic data, radiocarbon dates, fossil occurrences, and biogeographic range information among others. Including all relevant data into a single joint model is very challenging both conceptually and computationally. Advanced computational software packages that allow robust development of compatible (sub-)models which can be composed into a full model hierarchy have played a key role in these developments. Developing such software frameworks is increasingly a major scientific activity in its own right, and comes with specific challenges, from practical software design, development and engineering challenges to statistical and conceptual modelling challenges. BEAST 2 is one such computational software platform, and was first announced over 4 years ago. Here we describe a series of major new developments in the BEAST 2 core platform and model hierarchy that have occurred since the first release of the software, culminating in the recent 2.5 release.
Bayesian inference of phylogeny using Markov chain Monte Carlo (MCMC) (Drummond et al., 2002; Mau et al., 1999; Rannala and Yang, 1996) flourishes as a popular approach to uncover the evolutionary relationships among taxa, such as genes, genomes, individuals or species. MCMC approaches generate samples of model parameter values - including the phylogenetic tree -drawn from their posterior distribution given molecular sequence data and a selection of evolutionary models. Visualising, tabulating and marginalising these samples is critical for approximating the posterior quantities of interest that one reports as the outcome of a Bayesian phylogenetic analysis. To facilitate this task, we have developed the Tracer (version 1.7) software package to process MCMC trace files containing parameter samples and to interactively explore the high-dimensional posterior distribution. Tracer works automatically with sample output from BEAST (Drummond et al., 2012), BEAST2 (Bouckaert et al., 2014), LAMARC (Kuhner, 2006), Migrate (Beerli, 2006), MrBayes (Ronquist et al., 2012), RevBayes (Höhna et al., 2016) and possibly other MCMC programs from other domains.
Study region: Chihuahua, Coahuila, Nuevo Leon and Tamaulipas, Mexico; Texas, USA.
Study focus: The objective of this study is to identify and classify the transboundary hydrogeological units shared between Chihuahua, Coahuila, Nuevo Leon and Tamaulipas, Mexico, and Texas, and assess their potential transboundary linkages.
New hydrological insights: The transboundary groundwater resources between Mexico and United States are largely uncharacterized due to lack of data, differences in aquifer boundary delimitations and methodologies, and limited cooperation and coordination among federal and local agencies within and between countries to address groundwater challenges from a binational perspective. Our results indicate that the transboundary hydrogeological units identified cover around 180,000 km2 (110,000 km2 in Texas and 72,000 km2 in Mexico). Between 50% and 60% of this sharable area reports good aquifer potential and good water quality conditions. Some 20–25% is considered to have poor aquifer potential and water quality. The areas of the bolsons southeast of the Hueco-Tularosa Bolson Aquifer in northern Chihuahua and southwestern Texas, and between the Serrania del Burro and Allende-Piedras Negras Aquifers in southern Texas and northern Coahuila, appear to be the most important for transboundary aquifer potential. This study, the first assessment of its kind in this region, will support the development of transboundary management regimes aimed at preventing the degradation of future water supplies in the borderland between Mexico and United States.
“Transboundariness” refers to a new approach that identifies and prioritizes transboundary aquifers using socio-economic and political criteria, improving their characterization by using other variables in addition to their mere physical boundaries. This approach is applied to the hydrogeological units/aquifers shared by Mexico and Texas, with the following results. First, the rankings agree with the current level of attention to transboundary aquifers in the region by both countries, providing a quantifiable system that could be tested in other transboundary aquifers. Second, this approach provides a holistic and integrative perspective for transboundary aquifer assessment and prioritization. Third, this prioritization exercise expands the criteria currently used into a more integrative regime of groundwater links to the community as a whole. Finally, the results reflect not only how the transboundary aquifers are being used (or neglected) but also the socio-political context of the populations that depend on these resources for current and future development.
Studies on the distribution and evolution of organisms on oceanic islands have advanced towards a dynamic perspective1, where terrestrial endemicity results from island geographical aspects and geological history2 intertwined with sea-level fluctuations3,4. Diversification on these islands may follow neutral models5, decreasing over time as niches are filled6, or disequilibrium states7 and progression rules8, where richness and endemism rise with the age of the archipelago owing to the splitting of ancestral lineages (cladogenesis). However, marine organisms have received comparatively little scientific attention. Therefore, island and seamount evolutionary processes in the aquatic environment remain unclear9. Here we analyse the evolutionary history of reef fishes that are endemic to a volcanic ridge of seamounts and islands to understand their relations to island evolution and sea-level fluctuations. We also test how this evolutionary history fits island biogeography theory. We found that most endemic species have evolved recently (Pleistocene epoch), during a period of recurrent sea-level changes and intermittent connectivity caused by repeated aerial exposure of seamounts, a finding that is consistent with an ephemeral ecological speciation process10. Similar to findings for terrestrial biodiversity7, our data suggest that the marine speciation rate on islands is negatively correlated with immigration rate. However, because marine species disperse better than terrestrial species, most niches are filled by immigration: speciation increases with the random accumulation of species with low dispersal ability, with few opportunities for in situ cladogenesis and adaptive radiation. Moreover, we confirm that sea-level fluctuations and seamount location play a critical role in marine evolution, mainly by intermittently providing stepping stones for island colonization.
Background
Fish classifications, as those of most other taxonomic groups, are being transformed drastically as new molecular phylogenies provide support for natural groups that were unanticipated by previous studies. A brief review of the main criteria used by ichthyologists to define their classifications during the last 50 years, however, reveals slow progress towards using an explicit phylogenetic framework. Instead, the trend has been to rely, in varying degrees, on deep-rooted anatomical concepts and authority, often mixing taxa with explicit phylogenetic support with arbitrary groupings. Two leading sources in ichthyology frequently used for fish classifications (JS Nelson’s volumes of Fishes of the World and W. Eschmeyer’s Catalog of Fishes) fail to adopt a global phylogenetic framework despite much recent progress made towards the resolution of the fish Tree of Life. The first explicit phylogenetic classification of bony fishes was published in 2013, based on a comprehensive molecular phylogeny (www.deepfin.org). We here update the first version of that classification by incorporating the most recent phylogenetic results.
Results
The updated classification presented here is based on phylogenies inferred using molecular and genomic data for nearly 2000 fishes. A total of 72 orders (and 79 suborders) are recognized in this version, compared with 66 orders in version 1. The phylogeny resolves placement of 410 families, or ~80% of the total of 514 families of bony fishes currently recognized. The ordinal status of 30 percomorph families included in this study, however, remains uncertain (incertae sedis in the series Carangaria, Ovalentaria, or Eupercaria). Comments to support taxonomic decisions and comparisons with conflicting taxonomic groups proposed by others are presented. We also highlight cases were morphological support exist for the groups being classified.
Conclusions
This version of the phylogenetic classification of bony fishes is substantially improved, providing resolution for more taxa than previous versions, based on more densely sampled phylogenetic trees. The classification presented in this study represents, unlike any other, the most up-to-date hypothesis of the Tree of Life of fishes.
Electronic supplementary material
The online version of this article (doi:10.1186/s12862-017-0958-3) contains supplementary material, which is available to authorized users.
World experts of different disciplines, from molecular biology to macro-ecology, recognize the value of cave ecosystems as ideal ecological and evolutionary laboratories. Among other subterranean taxa, spiders stand out as intriguing model organisms for their ecological role of top predators, their unique adaptations to the hypogean medium and their sensitivity to anthropogenic disturbance. As the description of the first eyeless spider (Stalita taenaria), an array of papers on subterranean spider biology, ecology and evolution has been published, but a comprehensive review on these topics is still lacking. We provide a general overview of the spider families recorded in hypogean habitats worldwide, we review the different adaptations of hypogean spiders to subterranean life, and we summarize the information gathered so far about their origin, population structure, ecology and conservation status. Finally, we point out the limits of the knowledge we currently have regarding hypogean spiders, aiming to stimulate future research.
Aims The 50th anniversary of the publication of the seminal book, The Theory of Island Biogeography, by Robert H. MacArthur and Edward O. Wilson is a timely moment to review and identify key research foci that could advance island biology. Here, we take a collaborative horizon-scanning approach to identify 50 fundamental questions for the continued development of the field.
Location Worldwide.
Methods We adapted a well-established methodology of horizon scanning to identify priority research questions in island biology, and initiated it during the Island Biology 2016 conference held in the Azores. A multidisciplinary working group prepared an initial pool of 187 questions. A series of online surveys was
then used to refine a list of the 50 top priority questions. The final shortlist was restricted to questions with a broad conceptual scope, and which should be answerable through achievable research approaches.
Results Questions were structured around four broad and partially overlapping island topics, including: (Macro)Ecology and Biogeography, (Macro)Evolution, Community Ecology, and Conservation and Management. These topics were then subdivided according to the following subject areas: global diversity patterns (five questions in total); island ontogeny and past climate change (4); island rules and syndromes (3); island biogeography theory (4); immigration–speciation–extinction dynamics (5); speciation and diversification (4); dispersal and colonization (3); community assembly (6); biotic interactions (2); global change (5); conservation and management policies (5); and invasive alien species (4).
Main conclusions Collectively, this cross-disciplinary set of topics covering the 50 fundamental questions has the potential to stimulate and guide future research in island biology. By covering fields ranging from biogeography, community ecology and evolution to global change, this horizon scan has the potential to foster the formation of interdisciplinary research networks, enhancing joint efforts to better understand past, present and future of island biotas.
Background
Reconstructing phylogenies through Bayesian methods has many benefits, which include providing a mathematically sound framework, providing realistic estimates of uncertainty and being able to incorporate different sources of information based on formal principles. Bayesian phylogenetic analyses are popular for interpreting nucleotide sequence data, however for such studies one needs to specify a site model and associated substitution model. Often, the parameters of the site model is of no interest and an ad-hoc or additional likelihood based analysis is used to select a single site model. ResultsbModelTest allows for a Bayesian approach to inferring and marginalizing site models in a phylogenetic analysis. It is based on trans-dimensional Markov chain Monte Carlo (MCMC) proposals that allow switching between substitution models as well as estimating the posterior probability for gamma-distributed rate heterogeneity, a proportion of invariable sites and unequal base frequencies. The model can be used with the full set of time-reversible models on nucleotides, but we also introduce and demonstrate the use of two subsets of time-reversible substitution models. Conclusion
With the new method the site model can be inferred (and marginalized) during the MCMC analysis and does not need to be pre-determined, as is now often the case in practice, by likelihood-based methods. The method is implemented in the bModelTest package of the popular BEAST 2 software, which is open source, licensed under the GNU Lesser General Public License and allows joint site model and tree inference under a wide range of models.
PartitionFinder 2 is a program for automatically selecting best-fit partitioning schemes and models of evolution for phylogenetic analyses. PartitionFinder 2 is substantially faster and more efficient than version 1, and incorporates many new methods and features. These include the ability to analyze morphological datasets, new methods to analyze genome-scale datasets, new output formats to facilitate interoperability with downstream software, and many new models of molecular evolution. PartitionFinder 2 is freely available under an open source license and works on Windows, OSX, and Linux operating systems. It can be downloaded from www.robertlanfear.com/partitionfinder The source code is available at https://github.com/brettc/partitionfinder.
A very significant part of the world’s freshwater ichthyofauna is represented by ancient, exceptionally diverse and cosmopolitan ray-finned teleosts of the order Siluriformes. Over the years, catfish have been established as an exemplary model for probing historical biogeography at various scales. Yet, several tantalizing gaps still exist in their phylogenetic history, timeline and mode of diversification. Here, we re-examine the phylogeny of catfish by assembling and analyzing almost all publicly available mitogenome data. We constructed an ingroup matrix of 62 full-length mitogenome sequences from 20 catfish families together with four cypriniform outgroups, spanning 15,557 positions in total. Partitioned maximum likelihood analyses and Bayesian relaxed clock dating using fossil age constraints provide some useful and novel insights into the evolutionary history of this group. Loricarioidei are recovered as the first siluriform group to diversify, rendering Neotropics the cradle of the order. The next deepest clade is the South American Diplomystoidei placed as a sister group to all the remaining Siluroidei. The two multifamilial clades of “Big Asia” and “Big Africa” are also recovered, albeit nodal support for the latter is poor. Within “Big Asia”, Bagridae are clearly polyphyletic. Other interfamilial relationships, including Clariidae + Heteropneustidae, Doradidae + Auchenipteridae and Ictaluridae + Cranoglanididae are robustly resolved. Our chronogram shows that siluriforms have a Pangaean origin, at least as far back as the Early Cretaceous. The inferred timeline of the basal splits corroborates the “Out-of-South America” hypothesis and accords well with the fossil record. The divergence of Siluroidei most likely postdated the final separation of Africa and South America. An appealing case of phylogenetic affinity elaborated by biogeographic dispersal is exemplified by the Early Paleogene split between the Southeast Asian Cranoglanididae and Ictaluridae, with the latter radiating into North America’s freshwater realm by Eocene. The end of Cretaceous probably concludes the major bout of diversification at the family level while with the dawn of the Cenozoic a prolific radiation is evident at the generic level.
We investigated differentiation processes in the Neotropical fish Astyanax that represents a model system
for examining adaptation to caves, including regressive evolution. In particular, we analyzed microsatellite
and mitochondrial data of seven cave and seven surface populations from Mexico to test whether the
evolution of the cave fish represents a case of parallel evolution. Our data revealed that Astyanax invaded
northern Mexico across the Trans-Mexican Volcanic Belt at least three times and that populations of all
three invasions adapted to subterranean habitats. Significant differentiation was found between the cave
and surface populations. We did not observe gene flow between the strongly eye and pigment reduced
old cave populations (Sabinos, Tinaja, Pachon) and the surface fish, even when syntopically occurring like
in Yerbaniz cave. Little gene flow, if any, was found between cave populations, which are variable in eye
and pigmentation (Micos, Chica, Caballo Moro caves), and surface fish. This suggests that the variability is
due to their more recent origin rather than to hybridization. Finally, admixture of the young Chica cave
fish population with nuclear markers from older cave fish demonstrates that gene flow between populations
that independently colonized caves occurs. Thus, all criteria of parallel speciation are fulfilled.
Moreover, the microsatellite data provide evidence that two co-occurring groups with small sunken eyes
and externally visible eyes, respectively, differentiated within the partly lightened Caballo Moro karst
window cave and might represent an example for incipient sympatric speciation.
This article presents W-IQ-TREE, an intuitive and user-friendly web interface and server for IQ-TREE, an efficient phylogenetic
software for maximum likelihood analysis. W-IQ-TREE supports multiple sequence types (DNA, protein, codon, binary and morphology)
in common alignment formats and a wide range of evolutionary models including mixture and partition models. W-IQ-TREE performs
fast model selection, partition scheme finding, efficient tree reconstruction, ultrafast bootstrapping, branch tests, and
tree topology tests. All computations are conducted on a dedicated computer cluster and the users receive the results via
URL or email. W-IQ-TREE is available at http://iqtree.cibiv.univie.ac.at. It is free and open to all users and there is no login requirement.
The unique morphology of cave animals has interested biologists at least since the time of Lamarck. After a number of non-adaptive explanations for the morphology of cave animals, especially with respect to eye and pigment loss, a neo-Darwinian explanation, emphasizing constructive morphological changes rather than losses, was put forward by Barr, Christiansen, and Poulson in the 1960’s. Emphasizing convergent evolution (troglomorphy), this paradigm has recently been challenged, with evidence of divergent selection and the widespread occurrence of morphologically similar species in other subterranean habitats, including ones with abundant food and relatively strong environmental fluctuations. An emerging paradigm emphasizes the central role of darkness in convergent evolution, and the role of habitat size and interspecific competition in divergent evolution of subterranean species.
Sprememba paradigme o evoluciji jamskega življenja
Edinstvena morfologija jamskih živali, predvsem v povezavi z izgubo oči in pigmenta, je zanimala biologe že od časa Lamarcka. Kasneje so bile predstavljene tudi druge, t.im. neodarvinistične razlage, s poudarkom na konstruktivnih morfoloških spremembah namesto izgubah, povzete s strani Barra, Christiansena in Poulsona v 60. letih 20. stoletja. Z novejšimi raziskavami o divergentni selekciji in razširjeni prisotnosti morfološko podobnih vrst v drugih podzemeljskih habitatih, vključno s tistimi, kjer je veliko hrane in z relativno velikimi okoljskimi nihanji, se je zamajala paradigma, temelječa na konvergentni evoluciji (troglomorfija). Novo nastajajoča paradigma poudarja osrednjo vlogo teme v konvergentni evoluciji, ter vlogo velikosti habitata in medvrstne kompeticije v divergentni evoluciji podzemeljskih vrst.
David C. Culver & Tanja Pipan: Climate, abiotic factors, and the evolution of subterranean life Climate, and more generally the physical conditions in caves and other subterranean habitats have a profound influence on the biota. At longer time scale (centuries), climate change can force and/or isolate species in subterranean habitats. Not only Pleistocene climate changes, but earlier ones as well, such as the Messinian salinity crisis were important in this regard. While many speleobiologists assume that caves are nearly constant environmentally and with scarce organic carbon, this is not the case, especially in non-cave subterranean habitats. Many shallow subterranean habitats, such as epikarst, seepage springs, and talus harbor highly modified organisms, ones without eyes and pigment and with elongated appendages. Yet these habitats are highly variable with respect to temperature and other environmental factors, and often have high levels of organic carbon. Overall, the role of these shallow subterranean habitats in the evolution and biogeography of subterranean species may be crucial. On smaller spatial scales, environmental differences, such as differences in chemistry of epikarst water, may be important in allowing large numbers of species to coexist.
Significance
On several Alaskan islands, phenotypically variable threespine stickleback fish now live in ponds that were formed during uplift caused by the 1964 Great Alaska Earthquake. We analyzed phenotypic and genome-wide genetic divergence of resident freshwater and oceanic threespine stickleback populations from three islands. These data support the hypothesis that the freshwater populations evolved repeatedly from their oceanic ancestors in the past half-century, and have differentiated to nearly the same extent as populations that were founded thousands of years ago. This work raises the possibility that much of the evolution that occurs when oceanic stickleback invade fresh water takes place in fewer than 50 generations after colonization, rather than gradually over thousands of years.
The Eocene through Miocene Cypress Hills Formation of Saskatchewan and Alberta has been the basis of
studies on sedimentology, paleobotany, herpetofauna, avifauna, and mammalian local faunas. We describe the ichthyofauna from the Eastend area of the formation, representing late Eocene Chadronian to early Oligocene Whitneyan deposits. This fauna is diverse, including at least 14 fish taxa: Lepisosteus, Amiinae, aff. Hiodon, at least three cypriniforms among which is a Ptychocheilus-like leuciscine and at least one catostomid, two ictalurids, both ascribed to Astephus, a probable salmoniform, an amblyopsid-like percopsiform, Mioplosus, a probable moronid, a centrarchid, and at least one other perciform of uncertain affinity. The formation may therefore represent the first fossil record of the Amblyopsidae, and the first North American occurrence of the Moronidae. The composition of the ichthyofauna suggests higher temperatures during the Eocene–Oligocene transition than at present. Paleotemperatures similar to those of the Gulf Coast of the United States are indicated by the present ranges of several taxa, as well as by the large sizes attained by some of these fishes. The high relative abundance of abraded ictalurid material representing small individuals suggests that much of the formation was deposited in shallow, hypoxic floodplain pools that may have seasonally dried out. However, the large sizes attained by some taxa and the diversity of the fauna as a whole indicate that the neighboring aquatic environments were diverse, with welloxygenated, vegetated, permanent, and deep-water environments. This suggests the presence of a mosaic of conditions, such
as is found in large floodplains.
Large phylogenomics data sets require fast tree inference methods, especially for maximum-likelihood (ML) phylogenies. Fast
programs exist, but due to inherent heuristics to find optimal trees, it is not clear whether the best tree is found. Thus,
there is need for additional approaches that employ different search strategies to find ML trees and that are at the same
time as fast as currently available ML programs. We show that a combination of hill-climbing approaches and a stochastic perturbation
method can be time-efficiently implemented. If we allow the same CPU time as RAxML and PhyML, then our software IQ-TREE found
higher likelihoods between 62.2% and 87.1% of the studied alignments, thus efficiently exploring the tree-space. If we use
the IQ-TREE stopping rule, RAxML and PhyML are faster in 75.7% and 47.1% of the DNA alignments and 42.2% and 100% of the protein
alignments, respectively. However, the range of obtaining higher likelihoods with IQ-TREE improves to 73.3–97.1%. IQ-TREE
is freely available at http://www.cibiv.at/software/iqtree.
Since the early 1930s, a number of geologists prospecting for diamonds in the region of Singida in north-central Tanzania have reported the occurrence of superbly preserved fossils in lake beds overlying kimberlite pipes (Teale, 1931, 1932; Eades and Reeve, 1938; Williams, 1939; Greenwood, 1960; Mannard, 1962; Greenwood and Patterson, 1967). The sediments containing the fossils consist of shales and mudstones deposited in small crater lakes. These fossil localities have never been the subject of detailed paleontological investigation. As a consequence, in 1996 the senior author initiated excavations at the middle Eocene locality of Mahenge, the most productive fossil-bearing locality in the region (Greenwood, 1960; Mannard, 1962). The results of this expedition confirm the exceptional productivity and scientific importance of this site, and serve to highlight the paleontological potential of the region in general. A sizeable collection of fossil fishes, frogs, insects and plant remains was recovered. The fossils are remarkably well-preserved and, in the case of vertebrates, are generally represented by entire and articulated skeletons, occasionally preserving details of their soft anatomy (Greenwood, 1960; this report).
Lake Tanganyika is known for the endemicity of its fishes and species flocks of cichlids, Lates, mochokid catfishes and mastacembelid spiny eels. While the term “species flock” is sometimes applied to Tanganyika’s claroteine catfishes, the number of lineages represented among them and their extra-lacustrine affinities was unknown. Tanganyikan claroteines include three genera endemic to the Lake—Phyllonemus (3 spp.), Bathybagrus (1 sp.) and Lophiobagrus (4 spp.)—as well as seven endemic species referred to Chrysichthys, a widespread genus with more than 40 valid species across Africa. We conducted a phylogenetic study of 58 specimens representing 42 claroteine species using nuclear (rag2) and mitochondrial (cytochrome b) DNA sequences. We included one species of Phyllonemus, two species of Lophiobagrus, Bathybagrus tetranema, and six of the seven Tanganyikan endemic species of Chrysichthys (all but C. stappersii) along with 24 nominal species of Chrysichthys from central, western and eastern Africa drainages as well as Clarotes laticeps, Amarginops platus, Gephyroglanis congicus, Rheoglanis dendrophorus and undescribed taxa from the Congo basin. We find that the three Tanganyikan genera—Phyllonemus, Bathybagrus & Lophiobagrus—belong to a monophyletic group that includes five of the six Tanganyikan Chrysichthys sampled (C. grandis, C. graueri, C. platycephalus, C. sianenna, and C. acsiorum). This clade is most closely related to Clarotes laticeps, a species widely distributed in East Africa, the Nile, and West Africa. However, C. brachynema, the only claroteine in Lake Tanganyika with a well developed postcleithral process, belongs to a large clade of Congo basin species. Using the Eocene fossil claroteid †Chrysichthys mahengeensis and the inferred age of Lake Tanganyika as temporal calibrations, a Bayesian relaxed clock analysis in the software BEAST estimated that the impressive claroteine radiation in the Congo basin has taken place within the past 5 million years.
Se reconocen tres especies del grupo Ictalurus furcatus (género Ictalurus): I. furcatus, I. meridionalis e I. balsanus. Los caracteres diagnósticos de estas especies se encuentran en los huesos del esqueleto, en el conteo de vértebras y radios anales, en la morfometría y en la coloración. Ictalurus balsanus tiene un proceso más corto en el supraoccipital, en la placa anterior de la nuca y en el poscleitro; presenta escasas ornamentaciones en la espina de la aleta pectoral y un alargado proceso posterior del premaxilar. Ictalurus furcatus e I. meridionalis son especies muy similares pero se distinguen claramente por la ornamentación de la espina de la aleta pectoral, por la forma y textura del proceso supraoccipital y la forma del proceso postcleitral; así como, por el número de vértebras y radios anales y por la longitud de la aleta anal y del pedúnculo caudal. Las tres especies también presentan diferencias en la talla máxima y en la coloración del cuerpo. Los resultados del análisis del ADN mitocondrial (12S y 16S), de una muestra limitada, son compatibles con los resultados morfológicos: I. meridionalis es una especie distinta de I. furcatus; I. balsanus es la especie más divergente de las tres. I. furcatus e I. meridionalis presentan variaciones, entre cuencas hidrográficas, en cuanto al número de vértebras y radios de la aleta anal.
Long branch attraction is a prevalent form of bias in phylogenetic estimation but the reasons for it are only partially understood. We argue here that it is largely due to differences in the sizes of the model spaces corresponding to different trees. Trees with long branches together allow much more flexible internal branch-length parameter estimation. Consequently, although each tree has the same number of parameters, trees with long branches together have larger effective model spaces. The problem of long branch attraction becomes particularly pronounced with partitioned data. Formulation of tree estimation as model selection leads us to propose bootstrap bias corrections as cross-checks on estimation when long branches end up being estimated together.
Two cyprinid fishes from fossil deposits of Sumatra, Indonesia, were briefly described and named in 1876 as new species in extant genera. These taxa, despite being important early records for the family, have been excluded from later studies, probably because the cursory descriptions and lack of illustrations provided little data for other researchers. These two fish, Barbus megacephalus Günther and Thynnichthys amblyostoma von der Marck, are here fully described and illustrated. They are both removed from the extant genera and each is given its own new genus, as Sundabarbus megacephalus and Padangia amblyostoma. Both are assigned to the subfamily Barbinae (equivalent to the tribe Barbini). These two species are some of the oldest known members of the family, coming from deposits that are believed to be Eocene in age. © 2019, © The Trustees of the Natural History Museum, London 2019. All rights reserved.
Significance
Ray-finned fishes form the largest and most diverse group of vertebrates. Establishing their phylogenetic relationships is a critical step to explaining their diversity. We compiled the largest comparative genomic database of fishes that provides genome-scale support for previous phylogenetic results and used it to resolve further some contentious relationships in fish phylogeny. A vetted set of exon markers identified in this study is a promising resource for current sequencing approaches to significantly increase genetic and taxonomic coverage to resolve the tree of life for all fishes. Our time-calibrated analysis suggests that most lineages of living fishes were already established in the Mesozoic Period, more than 65 million years ago.
The Widemouth Blindcat, Satan eurystomus Hubbs and Bailey 1947, was the second of four stygobitic species of Ictaluridae discovered in the subterranean waters of southern Texas and northeastern Mexico. The skeletal anatomy of Satan has been scarcely known from a few, dated radiographs. Using additional radiographs and high resolution CT-datasets for two well-ossified specimens, we applied high-resolution X-ray computed tomography (HRXCT) to visualize, illustrate and describe the bony skeleton of Satan. We also provide an online archive of still and animated tomographic images of the skeletal anatomy of this little-known species. The skeleton and soft anatomy of Satan are distinctive. Twelve skeletal autapomorphies are described that singularly distinguish Satan within Ictaluridae and, probably in combination, from all other catfishes. Some of these are reductive losses or simplifications of skull bones (e.g. loss of one infraorbital bone; reduced ornamentation of the pterotic bone) and joint complexity (e.g. simple overlapping frontal-lateral ethmoid articulation; loosely ligamentous interopercle-posterior ceratohyal joint). Some of the autapomorphies are anatomically and perhaps developmentally complex (e.g. a novel series of three midline joints closing a middle span of the posterior cranial fontanel; a deeply excavated temporal fossa and an unusually enlarged interhyal bone). The tiny dorsal-fin spinelet (first lepidotrich) of Satan has a novel peaked and twisted shape. Ten apparent and exclusive synapomorphies within Ictaluridae gathered from this and previous studies suggest that Satan and Pylodictis are closest relatives. Most of these are functionally related to prey detection and suction feeding: fusion of the symphyseal mandibular sensory pores and increase in the number of preoperculo-mandibular canal pores; depressed, flattened heads and wide transverse mouths; prominent posterior process of the lateral ethmoid alongside and below the frontal bone margin; vertical and blade-like supraoccipital posterior process; unique arrangement of the parasagittal and occipital muscleattachment crests on the skull roof; large triangular panel of integument within the operculum framed by the opercle, preopercle and interopercle bones; elongated posterior ceratohyal; and, form of the fourth supraneural and loss of its anterior nuchal plate. In contrast, 15 synapomorphies recovered by Arce-H. et al. 2016, are confirmed suggesting that Satan is one of the four stygobitic ictalurids comprising a "Troglobites" subclade within the family: (Trogloglanis, Satan, Prietella phreatophila, P. lundbergi). These features include three stygomorphic and reductive apomorphies that are exclusive within Ictaluridae: loss of fully developed eyes and pigmentation, and simplification of the fifth vertebra and its joint with the Weberian apparatus. Twelve other synapomorphies shown by the Troglobites are also apparent homoplasies of character states shared with various other ictalurids. These include reductive characters such as shortened lateral line canal, reduced infraorbitals and underdeveloped or incomplete ossifications of the pterotic, supraoccipital, hyoid arch bones and transcapular ligament. Also, the Troglobites and various other ictalurids have: an adnate adiposecaudal fin, foreshortened anterior cranial fontanelle, reduced ventral wings of the frontal bone, replacement of bone by cartilage in hypohyal joints; incompletely ossified transcapular ligament, and consolidation of some hypural bones. Completing a full morphological character dataset across the Troglobites has been impeded by incomplete specimen preparations and study of P. lundbergi and to a lesser extent, P. phreatophila and Trogloglanis. © 2017 by the Academy of Natural Sciences of Drexel University.
The Mexican orogen is the expression in Mexico of the Cordilleran orogenic system. The orogen extends the length of Mexico, a distance of 2000 km from the state of Sonora in the northwest to the state of Oaxaca in the south. The Mexican orogen consists of (1) a western hinterland of accreted oceanic basinal rocks and magmatic arc rocks generally known as the Guerrero volcanic superterrane, (2) a foreland orogenic wedge, commonly termed the Mexican fold and thrust belt (MFTB), composed of imbricated and folded Upper Jurassic-Lower Cretaceous carbonate rocks and Upper Cretaceous foreland-basin strata, and (3) an assemblage of variably folded and inverted Late Cretaceous to Eocene foreland basins that lie northeast and east of the MFTB. The Mexican orogen encompasses the entire country, spanning several physiographic provinces and deformational domains that display both thin-skinned and thick-skinned structural styles determined by inherited crustal structure and contrasting pre-kinematic sedimentary sections. The orogen contains kinematic characteristics of both the Sevier and Laramide orogens in the United States (U.S.), and deformation in the Mexican orogen spanned the deformational history of those U.S. orogens. The overall trend of the Mexican orogen is NW-SE, although it displays local trend variations. At presently exposed levels, the orogen consists of folded and reverse-faulted Mesozoic-Eocene strata. Lower Cretaceous strata of the deformed foreland are dominated by carbonate rocks, whereas time-equivalent strata in the hinterland consist of deformed plutons belonging to one or more magmatic arcs, as well as turbidites, pillow lavas and altered mafic rocks deposited in an offshore basin prior to consolidation of fringing arc systems to mainland Mexico. Upper Cretaceous syntectonic strata of the foreland orogenic wedge constitute siliciclastic turbidite successions that grade eastward to carbonate pelagites of the distal foreland basin, which was starved of siliciclastic sediment input. Uppermost Cretaceous and Paleogene strata of the foreland basin constitute a shelfal, deltaic and coastal plain fluvial succession in northeastern Mexico and a succession of turbidites in the Tampico-Misantla basin east of the MFTB.
We performed the first combined-data phylogenetic analysis of ictalurids including most living and fossil species. We sampled 56 extant species and 16 fossil species representing outgroups, the seven living genera, and the extinct genus †Astephus long thought to be an ictalurid. In total, 209 morphological characters were curated and illustrated in MorphoBank from published and original work, and standardized using reductive coding. Molecular sequences harvested from GenBank for one nuclear and four mitochondrial genes were combined with the morphological data for total evidence analysis. Parsimony analysis recovers a crown clade Ictaluridae composed of seven living genera and numerous extinct species. The oldest ictalurid fossils are the Late Eocene members of Ameiurus and Ictalurus. The fossil clade †Astephus placed outside of Ictaluridae and not as its sister taxon. Previous morphological phylogenetic studies of Ictaluridae hypothesized convergent evolution of troglobitic features among the subterranean species. In contrast, we found morphological evidence to support a single clade of the four troglobitic species, the sister taxon of all ictalurids. This result holds whether fossils are included or not. Some previously published clock-based age estimates closely approximate our minimum ages of clades.
Divergence-time estimation based on molecular phylogenies and the fossil record has provided insights into fundamental questions of evolutionary biology. In Bayesian node dating, phylogenies are commonly time calibrated through the specification of calibration densities on nodes representing clades with known fossil occurrences. Unfortunately, the optimal shape of these calibration densities is usually unknown and they are therefore often chosen arbitrarily, which directly impacts the reliability of the resulting age estimates. As possible solutions to this problem, two non-exclusive alternative approaches have recently been developed, the “fossilized birth-death” model and “total-evidence dating”. While these approaches have been shown to perform well under certain conditions, they require including all (or a random subset) of the fossils of each clade in the analysis, rather than just relying on the oldest fossils of clades. In addition, both approaches assume that fossil records of different clades in the phylogeny are all the product of the same underlying fossil sampling rate, even though this rate has been shown to differ strongly between higher-level taxa. We here develop a flexible new approach to Bayesian age estimation that combines advantages of node dating and the fossilized birth-death model. In our new approach, calibration densities are defined on the basis of first fossil occurrences and sampling rate estimates that can be specified separately for all clades. We verify our approach with a large number of simulated datasets, and compare its performance to that of the fossilized birth-death model. We find that our approach produces reliable age estimates that are robust to model violation, on par with the fossilized birth-death model. By applying our approach to a large dataset including sequence data from over 1000 species of teleost fishes as well as 147 carefully selected fossil constraints, we recover a timeline of teleost diversification that is incompatible with previously assumed vicariant divergences of freshwater fishes. Our results instead provide strong evidence for trans-oceanic dispersal of cichlids and other groups of teleost fishes.
GenBank® (www.ncbi.nlm.nih.gov/genbank/) is a comprehensive database that contains publicly available nucleotide sequences for over 340 000 formally described species. Recent developments include a new starting page for submitters, a shift toward using accession.version identifiers rather than GI numbers, a wizard for submitting 16S rRNA sequences, and an Identical Protein Report to address growing issues of data redundancy. GenBank organizes the sequence data received from individual laboratories and largescale sequencing projects into 18 divisions, and Gen Bank staff assign unique accession.version identifiers upon data receipt. Most submitters use the web-based BankIt or standalone Sequin programs. Daily data exchange with the European Nucleotide Archive (ENA) and the DNA Data Bank of Japan (DDBJ) ensures worldwide coverage. GenBank is accessible through the nuccore, nucest, and nucgss databases of the Entrez retrieval system, which integrates these records with a variety of other data including taxonomy nodes, genomes, protein structures, and biomedical journal literature in PubMed. BLAST provides sequence similarity searches of GenBank and other sequence databases. Complete bimonthly releases and daily updates of the GenBank database are available by FTP.
The transboundary nature of water dividing Mexico and the United States (U.S.) transforms the entire border region into an instrument of cooperation, a source of conflict, a national security issue, and an environmental concern. Reasonable data collection and research analysis have been conducted for surface waters by joint governmental institutions and non-governmental bodies. However, with the exception of the U.S. Transboundary Assessment Act Program (TAAP) (focusing on the Hueco Bolson, Mesilla Bolson, San Pedro and Santa Cruz aquifers), there is no comparable research, institutional development, or assessment of transboundary groundwater issues on the frontier. Moreover, data collection and methodologies vary between the two countries, there is no broadly accepted definition of the transboundary nature of an aquifer, and available legal and policy frameworks are constrained by non-hydrological considerations. Hence, there is a conceptual and institutional void regarding transboundary groundwater resources between Mexico and the U.S. The purpose of this paper is to bridge this void and characterize transboundary aquifers on the Mexico-US border. It reviews existing international frameworks for identifying hydrological and social criteria that characterize an aquifer as transboundary. It then assesses data from both countries to propose where and which aquifers could be considered transboundary. Finally, the paper proposes an agenda for assessing Mexico-US transboundary aquifers as a means for improving groundwater management in the border region.
This book had its origin when, about five years ago, an ecologist (MacArthur) and a taxonomist and zoogeographer (Wilson) began a dialogue about common interests in biogeography. The ideas and the language of the two specialties seemed initially so different as to cast doubt on the usefulness of the endeavor. But we had faith in the ultimate unity of population biology, and this book is the result. Now we both call ourselves biogeographers and are unable to see any real distinction between biogeography and ecology.
For the past 70 years only one species of flathead bullhead, Ictalurus platycephalus (Girard), has been recognized in the southeastern United States. Critical study has revealed the existence of three distinct species. I. platycephalus is redescribed; it is confined to the Atlantic coast from Virginia to Georgia. I. brunneus (Jordan) is sympatric over much of the range of I. platycephalus, and also occurs in the St. Johns River of Florida and in the Apalachicola River on the Gulf Coast. It is distinguished from the former species by a shorter anal fin with fewer rays, a higher number of gill rakers, as well as other morphological features and ecological requirements. I. serracanthus is described as a new species from the Gulf Coastal Plain of Florida, Georgia, and Alabama. It is characterized by light-colored round spots, large serrations on the pectoral spines, and a narrow black margin on the pectoral fin membranes. It appears to be more closely related to the white catfish, Ictalurus catus, than to the other flat-headed species, and apparently evolved in the limestone region of northern Florida, an area of endemism. A theory for the origins and dispersal of I. platycephalus and I. brunneus is proposed, based on the confluence of drainage systems during periods of lowered sea level, and on stream captures in the southern Appalachians.
Two additional specimens of Satan eurystomus Hubbs and Bailey and one additional specimen of Trogloglanis pattersoni Eigenmann are described. New evidence on relationships is also presented.
The blind catfishes Trogloglanis pattersoni and Satan eurystomus occur in deep artesian waters of the Edwards Aquifer in southwest Texas. The origin of their cavernicolous evolution was traced back to Pliocene or Miocene. Both blindcats exhibit extreme and uniform regressions of pigmentation, eyes and their correlated brain centers, and the pineal organ. They also evolved a hypertrophy of the saccus vasculosus, the telencephalon, and the cerebellum. The effects of high hydrostatic pressure are reflected by the evolution of the morphological "deep sea syndrome" in both blindcats. They exhibit a total regression of the swimbladder, an accumulation of large adipose deposits, and furthermore a series of apparently paedomorphic traits: a small body size, an enlarged head, a weakly ossified skeleton, and reduced muscles. Besides these convergent adaptations, both species differ in morphological features that suggest adaptations to distinct ecological niches.
Prietella lundbergi, a new species of cave ictalurid and only the second of the genus to be discovered, is described from a single specimen collected in a subterranean thermal spring, Tamaulipas state, México. Morphologically, the new species shares with three previously known troglobitic ictalurids (Prietella phreatophila, Satan eurystomus, Trogloglanis pattersoni) many convergent, paedomorphic characters associated with subterranean life. Prietella lundbergi differs from its nearest relative, P. phreatophila, in retention of the endopterygoid; reduction of the swimbladder; hypural osteology; numbers of principal caudalfin rays, branchiostegals and gill rakers; and in some body measurements. Morphological comparisons support monophyly of the genus Prietella and its recognition as the sister group of Noturus. The new species is found in the El Abra mountains of the Sierra Madre Oriental range, far outside the Río Grande basin and Edwards Aquifer where all other ictalurid troglobites occur. Historical interdrainage connections along the northeast Gulf Coastal Plain of México may have favored a broad distribution of the epigean ancestor of the two extant Prietella species. /// Se describe una nueva especie de bagre ciego ictalurido, Prietella lundbergi, en base a un solo ejemplar capturado en un fuente subterráneo con aguas cálidas en el estado Tamaulipas, México. Antes del este descubrimiento nuevo, el género Prietella se habia conocido por una sola especie, P. phreatophila. Esta especie nueva posee varios carácteres morfológicos convergentes y paedomórficos en común con las otras tres especies de ictaluridos conocidos con hábitos troglobios (Prietella phreatophila, Satan eurystomus y Trogloglanis pattersoni). Prietella lundbergi se distingue de P. phreatophila por la retención de los huesos endopterigoides; la reducción de la vejiga gaseosa; la osteología del base de la aleta caudal; el número de radiales de la aleta caudal; los números de los radios branquiostegios y branquispinas del primer arco branquial; y tambien por varias medidas morfométricas. Una comparación morfológico presenta evidencia que Prietella forman un grupo "sister" monofilético del género Noturus. La localidad tipica de de la especie nueva es una cueva situada en las montañas El Abra de la Sierra Madre Oriental. Esta localidad está ubicado bastante lejos de la cuenca del Río Grande y Edwards Aquifer de donde se encuentran los otros tres ictaluridos adaptados a la vida en las aguas subterráneas. Se proponen que la interconexión histórica entre los varios dranajes en el parte noreste del costo plano del Golfo de México ha permitodo el ancestro de las dos especies de Prietella a tener una distribución posteriormente muy amplia.
The evolution of the holarctic cave Collembola of the subfamily Entomobryinae is analyzed. A number of evolutionary lines are shown, involving the two polyphyletic genera Pseudosinella and Sinella in Japan, North America, and Europe. Characteristics of these animals are of two types: cave dependent (responding rapidly to the cave environment) and cave independent (showing no effect of the cave environment). The evolution of the cave organisms is divided into three stages. The first stage represents the level of adaptation normally found in troglophile organisms, although some troglobites are found in the stage. All such forms are very limited in their cave distribution, and occupy a few caves around the periphery of major cave habitats. The second stage of evolution shows more cave adaptation, but the evolutionary pathways are varied, with convergence, parallelism, and divergence common. Most forms within this stage are troglobites, but there are a few troglophiles, and many of the organs characteristic of the stage occur as preadaptations in some putative ancestral forms. The members of this stage are abundant and relatively widespread. Within the third evolutionary stage convergence is universal, and the organs characteristic of these forms are limited to cave members of the family. Forms falling within this stage are relatively abundant but extremely limited in distribution. The probable adaptive significance of several organ modifications characteristic of troglobite forms is discussed, and these structures are interpreted as positive adaptations to the new requirements of cave life which have the final result of closely limiting the animals to the cave environment.
A low diversity trace fossil assemblage is described from the Oligocene Sawahlunto Formation near Kandi, in the northwestern part of the Ombilin Basin in western Sumatra, Indonesia. This trace fossil assemblage includes six ichnogenera attributed to invertebrate infaunal and epifaunal activities (Arenicolites, Diplocraterion, Planolites, Monocraterion/Skolithos and Coenobichnus) and two ichnotaxa attributed to vertebrate activity (avian footprints: two species of Aquatilavipes). Arenicolites, Diplocraterion and Monocraterion/Skolithos record the suspension feeding activities of either arthropods (most likely amphipods) or vermiform organisms. Planolites reflects the presence of an infaunal deposit feeder. Coenobichnus records the walking activities of hermit crabs. Both the Coenobichnus and the avian footprints record the surficial detritus scavenging of epifaunal organisms within a subaerial setting. These traces occur within a fine-grained sandstone succession characterized by planar laminae and low-relief, asymmetrical, commonly mud-draped (locally bidirectional) ripples.The presence of traces attributable to suspension feeders implies deposition in a subaqueous setting. Their occurrence (particularly the presence of Arenicolites and Diplocraterion) in a sandstone bed characterized by mud-draped and bidirectional ripples implies emplacement in a tidally-influenced marine to marginal marine setting. Co-occurrence of these traces with well-preserved avian footprints (Aquatilavipes) further implies periodic subaerial exposure. Thus, it is most likely that the Sawahlunto Formation near Kandi records deposition within an intertidal flat setting. Definitive evidence of marine influences in the Oligocene interval of the Ombilin Basin implies a more complex tectono-stratigraphic history than has previously been implied.