Stable isotopes are becoming an increasingly powerful tool for studying the physiological ecology of animals. The (13)C/(12)C ratios of animal tissues are frequently used to reconstruct the diet of animals. This usually requires killing the subjects. While there is an extensive medical literature on measuring the (13)C/(12)C ratio of exhaled CO(2) to determine substrate digestion and oxidation, we found little evidence that animal physiologists or physiological ecologists have applied (13)C/(12)C breath analysis in their studies. The analysis breath (13)C/(12)C ratios has the advantage of being non-invasive and non-destructive and can be repeatedly used on the same individual. Herein we briefly discuss the medical literature. We then discuss research which shows that, not only can the breath(13)C/(12)C ratio indicate what an animal is currently eating, but also the animal's diet in the past, and any changes in diet have occurred over time. We show that naturally occurring (13)C/(12)C ratios in exhaled CO(2) provides quantitative measure of the relative contribution of carbohydrates and lipids to flight metabolism. This technique is ripe for application to field research, and we encourage physiological ecologists to add this technique to their toolbox.
Dense aggregations of tube-worms can stabilize sediments and generate oases for benthic communities that are different and often more diverse and abundant than those of the surroundings. If these features are to qualify as biogenic reefs under nature-conservation legislation such as the EC Habitats Directive, a level of stability and longevity is desirable aside from physical and biological attributes. Lanice conchilega (Pallas, 1766) is widely distributed around the European coast and aggregations of this tube-dwelling polychaete are known to have a positive effect on the biodiversity of associated species in inter- and sub-tidal areas. This increases the value of L. conchilega-rich habitats for higher trophic levels such as birds and fish. However, L. conchilega is currently not recognized as a reef builder primarily due to uncertainty about the stability of their aggregations. We carried out three studies on different spatial and temporal scales to explore a number of properties relating to stability: (1) Individual aggregations of L. conchilega of ∼1 m(2) were monitored for up to 1 year, (2) records of L. conchilega from a 258-ha area over a 35-year period were analyzed, (3) the recovery of a population of L. conchilega subjected to disturbances by cultivation of Manila clams (Ruditapes philippinarum) was followed over 3 years. The studies provided evidence about the longevity of L. conchilega aggregations, their resistance to disturbance, their resilience in recovering from negative impact and their large-scale persistence. The results showed that populations of L. conchilega were prone to considerable fluctuation and the stability of aggregations depended on environmental factors and on recruitment. The tube-worms proved to be susceptible to disturbance by cultivation of Manila clams but demonstrated the potential to recover from that impact. The long-term monitoring of a large L. conchilega population in the Bay of Mont Saint Michel (France) indicated that aggregations can persist over many decades with a constant, densely populated core area and an expanding and contracting more thinly populated fringe zone. The stability of aggregations of L. conchilega and the structures they form do not unequivocally fit the currently accepted definition of a reef. However, given L. conchilega's accepted reef-like potential to influence diversity and abundance in benthic communities, we suggest clarifying and expanding the definition of reefs so that species with records of significant persistence in particular areas and which otherwise meet expectations of reefs are included within the definition.
The most diverse and species-rich class of the phylum Porifera is Demospongiae. In recent years, the systematics of this clade, which contains more than 7000 species, has developed rapidly in light of new studies combining molecular and morphological observations. We add more than 500 new, nearly complete 18S sequences (an increase of more than 200%) in an attempt to further enhance understanding of the phylogeny of Demospongiae. Our study specifically targets representation of type species and genera that have never been sampled for any molecular data in an effort to accelerate progress in classifying this diverse lineage. Our analyses recover four highly supported subclasses of Demospongiae: Keratosa, Myxospongiae, Haploscleromorpha, and Heteroscleromorpha. Within Keratosa, neither Dendroceratida, nor its two families, Darwinellidae and Dictyodendrillidae, are monophyletic and Dictyoceratida is divided into two lineages, one predominantly composed of Dysideidae and the second containing the remaining families (Irciniidae, Spongiidae, Thorectidae, and Verticillitidae). Within Myxospongiae, we find Chondrosida to be paraphyletic with respect to the Verongida. We amend the latter to include species of the genus Chondrosia and erect a new order Chondrillida to contain remaining taxa from Chondrosida, which we now discard. Even with increased taxon sampling of Haploscleromorpha, our analyses are consistent with previous studies; however, Haliclona species are interspersed in even more clades. Haploscleromorpha contains five highly supported clades, each more diverse than previously recognized, and current families are mostly polyphyletic. In addition, we reassign Janulum spinispiculum to Haploscleromorpha and resurrect Reniera filholi as Janulum filholi comb. nov. Within the large clade Heteroscleromorpha, we confirmed 12 recently identified clades based on alternative data, as well as a sister-group relationship between the freshwater Spongillida and the family Vetulinidae. We transfer Stylissa flabelliformis to the genus Scopalina within the family Scopalinidae, which is of uncertain position. Our analyses uncover a large, strongly supported clade containing all heteroscleromorphs other than Spongillida, Vetulinidae, and Scopalinidae. Within this clade, there is a major division separating Axinellidae, Biemnida, Tetractinellida, Bubaridae, Stelligeridae, Raspailiidae, and some species of Petromica, Topsentia, and Axinyssa from Agelasida, Polymastiidae, Placospongiidae, Clionaidae, Spirastrellidae, Tethyidae, Poecilosclerida, Halichondriidae, Suberitidae, and Trachycladus. Among numerous results: (1) Spirophorina and its family Tetillidae are paraphyletic with respect to a strongly supported Astrophorina within Tetractinellida; (2) Agelasida is the earliest diverging lineage within the second clade listed above; and (3) Merlia and Desmacella appear to be the earliest diverging lineages of Poecilosclerida.
A stable phylogenetic hypothesis for families within jellyfish class Scyphozoa has been elusive. Reasons for the lack of resolution of scyphozoan familial relationships include a dearth of morphological characters that reliably distinguish taxa and incomplete taxonomic sampling in molecular studies. Here, we address the latter issue by using maximum likelihood and Bayesian methods to reconstruct the phylogenetic relationships among all 19 currently valid scyphozoan families, using sequence data from two nuclear genes: 18S and 28S rDNA. Consistent with prior morphological hypotheses, we find strong evidence for monophyly of subclass Discomedusae, order Coronatae, rhizostome suborder Kolpophorae and superfamilies Actinomyariae, Kampylomyariae, Krikomyariae, and Scapulatae. Eleven of the 19 currently recognized scyphozoan families are robustly monophyletic, and we suggest recognition of two new families pending further analyses. In contrast to long-standing morphological hypotheses, the phylogeny shows coronate family Nausithoidae, semaeostome family Cyaneidae, and rhizostome suborder Daktyliophorae to be nonmonophyletic. Our analyses neither strongly support nor strongly refute monophyly of order Rhizostomeae, superfamily Inscapulatae, and families Ulmaridae, Catostylidae, Lychnorhizidae, and Rhizostomatidae. These taxa, as well as familial relationships within Coronatae and within rhizostome superfamily Inscapulatae, remain unclear and may be resolved by additional genomic and taxonomic sampling. In addition to clarifying some historically difficult taxonomic questions and highlighting nodes in particular need of further attention, the molecular phylogeny presented here will facilitate more robust study of phenotypic evolution in the Scyphozoa, including the evolution characters associated with mass occurrences of jellyfish.
The parasitic isopod Orthione griffenis Markham, 2004 was originally described from thalassinid mud shrimp hosts collected in Oregon. Subsequently, O. griffenis has been cited as a non-indigenous species in estuaries of the Pacific Northwest of North America; however, no taxonomic work has provided evidence that specimens from the western coast of the United States and other localities are conspecific. We report the first record of O. griffenis from Chinese waters based on collections made in the 1950s, which pre-date any records of the species from the United States by at least 20 years. Females of the Chinese specimens match the original description except in the number of articles on antennae 2 (six and five articles in the Chinese material and holotype, respectively). However, newly examined material from the United States showed females are variable in this character, exhibiting 5-6 articles on antennae 2. Although males of O. griffenis from Oregon were originally described as having second antennae with five articles, reexamination of the allotype showed that antennae 2 were damaged and missing terminal articles. Thus, the number of articles in the second antennae of males is six, as found in both the Chinese and new samples from the United States. Scanning electron microscopy (SEM) of males from USA and China revealed curled setae on the distolateral margins of the uropods, which were not reported in the original description. In China the species is found on Austinogebia wuhsienweni (Yu) from Shandong province, whereas along the western coast of North America the species extends from British Columbia to California on Upogebia pugettensis (Dana) and U. macginitieorum Williams (the latter species replacing U. pugettensis south of Pt. Conception, California). Orthione griffenis has also been reported from Japan on Upogebia issaeffi (Balss) and Austinogebia narutensis (Sakai). In Coos Bay, Oregon, the prevalence of the species was ∼65% in the mature U. pugettensis. The species was presumably introduced as larvae released in ballast water from ships originating in Asia. The epicaridium larvae of O. griffenis were examined with SEM, and aspects of the life history of the species are reviewed.
Canada is a northern country. Whether defined in terms of geography, climate, culture, or political boundaries, the North is an integral part of Canadian national identity and a strategic component of the country’s future (Coates, 1995). Often defined as the half of the landmass and water that lies above the line of discontinuous permafrost, extending from northern British Columbia to Labrador, this vast region is home to only 1% of the human population in Canada. However, many other species are endemic to the North and many more seasonal migrants depend on northern environments for a significant part of their life history. The Canadian North, and indeed the entire circumpolar region, is a sensitive environment, facing rapid and unprecedented social, biophysical, and environmental changes. Several long-term, persistent, and pervasive changes are affecting northern environments simultaneously. Global climate change, ozone depletion, long-distance transport of contaminants, and rapid economic development have placed undue stress on terrestrial, freshwater and marine ecosystems. These stressors may have a wide range of ecologically significant effects on populations that will cascade upwards to affect the integrity of entire communities. World demand for energy supplies has increased interest in Canada’s northern oil and gas fields with the resultant prospect of a pipeline snaking down the Mackenzie River becoming ever closer to reality. The Canadian North is also the world’s third largest producer of diamonds, and mining for these precious stones now accounts for 20% of the Northwest Territories economic activity (McDonald, 2004). At the same time, new governance realities are being shaped by the settlement of aboriginal land claims and devolution of federal government responsibilities to the territories. These stressors and changes are a great cause of concern for aboriginal peoples as their health is affected by the consumption of country foods and their culture is linked to their desire to maintain traditional livelihoods. Nevertheless, much of the Canadian North is still in a natural, relatively undisturbed state, where most wildlife species are intact in terms of population abundance, distribution, and movement, and their hab1 From the Symposium Biology of the Canadian Arctic: A Crucible for Change in the 21st Centurypresented at the Annual Meeting of the Society for Integrative and Comparative Biology, 4‐8 January 2003, at Toronto, Canada.
Laboratory models have suggested a link between metabolism and life span in vertebrates, and it is well known that the evolution of specific life histories can be driven by metabolic factors. However, little is known regarding how the adoption of specific life-history strategies can shape aging and life span in populations facing different energetic demands from either a theoretical or a mechanistic viewpoint but significant insight can be gained by using a comparative approach. Comparative biology plays several roles in our understanding of the virtually ubiquitous phenomenon of aging in animals. First, it provides a critical evaluation of broad hypotheses concerning the evolutionary forces underlying the modulation of aging rate. Second, it suggests mechanistic hypotheses about processes of aging. Third, it illuminates particularly informative species because of their exceptionally slow or rapid aging rates to be interrogated about potentially novel mechanisms of aging. Although comparative biology has played a significant role in research on aging for more than a century, the new comparative biology of aging is poised to dwarf those earlier contributions, because: (1) new cellular and molecular techniques for investigating novel species are in place and more are being continually generated, (2) molecular systematics has resolved the phylogenetic relationships among a wide range of species, which allow for the implementation of analytic tools specialized for comparative biology, and (3) in addition to facilitating the construction of accurate phylogenies, the dramatic acceleration in DNA-sequencing technology is providing us with new tools for a comparative genomic approach to understanding aging.
Top pelagic predators such as tunas, sharks, marine turtles and mammals have historically been difficult to study due to their large body size and vast range over the oceanic habitat. In recent years the development of small microprocessor-based data storage tags that are surgically implanted or satellite-linked provide marine researchers a novel avenue for examining the movements, physiology and behaviors of pelagic animals in the wild. When biological and physical data obtained from the tags are combined with satellite derived sea surface temperature and ocean color data, the relationships between the movements, behaviors and physical ocean environment can be examined. Tag-bearing marine animals can function as autonomous ocean profilers providing oceanographic data wherever their long migrations take them. The biologging science is providing ecological physiologists with new insights into the seasonal movements, habitat utilization, breeding behaviors and population structures in of marine vertebrates. In addition, the data are revealing migration corridors, hot spots and physical oceanographic patterns that are key to understanding how organisms such as bluefin tunas use the open ocean environment. In the 21st century as ecosystem degradation and global warming continue to threaten the existence of species on Earth, the field of physiological ecology will play a more pivotal role in conservation biology.
Hormones coordinate developmental, physiological, and behavioral processes within and between all living organisms. They orchestrate and shape organogenesis from early in development, regulate the acquisition, assimilation, and utilization of nutrients to support growth and metabolism, control gamete production and sexual behavior, mediate organismal responses to environmental change, and allow for communication of information between organisms. Genes that code for hormones; the enzymes that synthesize, metabolize, and transport hormones; and hormone receptors are important targets for natural selection, and variation in their expression and function is a major driving force for the evolution of morphology and life history. Hormones coordinate physiology and behavior of populations of organisms, and thus play key roles in determining the structure of populations, communities, and ecosystems. The field of endocrinology is concerned with the study of hormones and their actions. This field is rooted in the comparative study of hormones in diverse species, which has provided the foundation for the modern fields of evolutionary, environmental, and biomedical endocrinology. Comparative endocrinologists work at the cutting edge of the life sciences. They identify new hormones, hormone receptors and mechanisms of hormone action applicable to diverse species, including humans; study the impact of habitat destruction, pollution, and climatic change on populations of organisms; establish novel model systems for studying hormones and their functions; and develop new genetic strains and husbandry practices for efficient production of animal protein. While the model system approach has dominated biomedical research in recent years, and has provided extraordinary insight into many basic cellular and molecular processes, this approach is limited to investigating a small minority of organisms. Animals exhibit tremendous diversity in form and function, life-history strategies, and responses to the environment. A major challenge for life scientists in the 21st century is to understand how a changing environment impacts all life on earth. A full understanding of the capabilities of organisms to respond to environmental variation, and the resilience of organisms challenged by environmental changes and extremes, is necessary for understanding the impact of pollution and climatic change on the viability of populations. Comparative endocrinologists have a key role to play in these efforts.
Functional morphology has benefited greatly from the input of techniques and thinking from other disciplines. This has been especially productive in situations where each discipline has made significant contributions to a particular research topic. A combination of methodologies from functional morphology and developmental biology has allowed us to characterize feeding mechanics of first-feeding larval zebrafish (Danio rerio). Contrary to kinematic patterns commonly seen in adult teleosts, larval zebrafish showed no lateral abduction during the expansive phase of a suction-feeding event. Instead, dorsoventral expansion of the buccal chamber, more typical of patterns seen in primitive fishes, characterized the expansive phase. Moreover, a pronounced preparatory phase during which the buccal chamber is constricted by the protractor hyoideus was consistently seen in first-feeding larval kinematics. Key kinematic variables associated with first feeding correlated significantly with the hydrodynamic regime as measured by the Reynolds number. Using the tools of both functional morphology and developmental biology we have not only determined which cranial muscles are important for successful feeding but also uncovered important physiological differences in muscle structure. Muscles necessary for the rapid dorsoventral expansion of the head are composed primarily of fast-twitch fibers while those involved in more tonic contractions such as hyoid protraction have more slow-twitch muscle fibers. While most evolutionary developmental studies have examined mechanisms responsible for large evolutionary changes in morphology, we propose that the type of data uncovered in functional studies can lead to the generation of hypotheses concerning the developmental mechanisms responsible for smaller intra- and/or interspecific changes.
The highly collaborative research sponsored by the NSF-funded Assembling the Porifera Tree of Life (PorToL) project is providing insights into some of the most difficult questions in metazoan systematics. Our understanding of phylogenetic relationships within the phylum Porifera has changed considerably with increased taxon sampling and data from additional molecular markers. PorToL researchers have falsified earlier phylogenetic hypotheses, discovered novel phylogenetic alliances, found phylogenetic homes for enigmatic taxa, and provided a more precise understanding of the evolution of skeletal features, secondary metabolites, body organization, and symbioses. Some of these exciting new discoveries are shared in the papers that form this issue of Integrative and Comparative Biology. Our analyses of over 300 nearly complete 28S ribosomal subunit gene sequences provide specific case studies that illustrate how our dataset confirms new hypotheses of sponge evolution. We recovered monophyletic clades for all 4 classes of sponges, as well as the 4 major clades of Demospongiae (Keratosa, Myxospongiae, Haploscleromorpha, and Heteroscleromorpha), but our phylogeny differs in several aspects from traditional classifications. In most major clades of sponges, families within orders appear to be paraphyletic. Although additional sampling of genes and taxa are needed to establish whether this pattern results from a lack of phylogenetic resolution or from a paraphyletic classification system, many of our results are congruent with those obtained from 18S ribosomal subunit gene sequences and complete mitochondrial genomes. These data provide further support for a revision of the traditional classification of sponges.
Models of the evolution of virulence have typically focused on increased mortality, one of two negative effects that parasites can inflict on their host. Those that consider the other effect, fecundity reduction, can predict that parasites should completely sterilize their hosts. Although this prediction seems extreme, sterilization features prominently in a fascinating strategy, parasitic castration. Such castration can be accompanied by gigantism (unusually large growth of infected hosts), long infectious periods, and fecundity compensation (where, before heavy parasite burdens ensue, newly infected hosts reproduce earlier/more than they would if not infected). Using a model of dynamic energy budgets (DEB), we show how these results readily emerge, assuming that parasites consume energy reserves of the host. The simple, but mechanistic, DEB model follows energy flow though hosts and parasites, starting with ingestion, and continuing with storage of assimilated energy, and use of those reserves for growth and reproduction, as allocated by the host according to the "κ-rule". Using this model, we compare and contrast two strategies for parasites. "Consumers" only steal energy from their hosts, thereby indirectly altering allocation of energy to growth and reproduction, reducing fecundity, and enhancing mortality. "Castrators" steal energy but also directly modify the scheme by which hosts allocate reserve energy, shunting resources from reproduction to growth. Not surprisingly, the model predicts that this strategy should promote gigantism, but it also forecasts longer infectious periods and fecundity compensation. Thus, commonly observed characteristics of parasitic castration readily emerge from a mechanistic model of energy flow using a minimal number of assumptions. Finally, the DEB model for both "consumers" and "castrators" highlight that variation in resources supplied to hosts promotes variation in virulence in a given host-parasite system, holding all else equal. Such predictions highlight the potential importance of resource ecology for virulence in disease systems.
The Gulf killifish, Fundulus grandis, is a small teleost fish that inhabits marshes of the Gulf of Mexico and demonstrates high tolerance of environmental variation, making it an excellent subject for the study of physiological and molecular adaptations to environmental stress. In the present study, two-dimensional (2D) gel electrophoresis and matrix-assisted laser desorption/ionization time-of-flight tandem mass spectrometry were used to resolve and identify proteins from five tissues: skeletal muscle, liver, brain, heart, and gill. Of 864 protein features excised from 2D gels, 424 proteins were identified, corresponding to a 49% identification rate. For any given tissue, several protein features were identified as the same protein, resulting in a total of 254 nonredundant proteins. These nonredundant proteins were categorized into a total of 11 molecular functions, including catalytic activity, structural molecule, binding, and transport. In all tissues, catalytic activity and binding were the most highly represented molecular functions. Comparing across the tissues, proteome coverage was lowest in skeletal muscle, due to a combination of a low number of gel spots excised for analysis and a high redundancy of identifications among these spots. Nevertheless, the identification of a substantial number of proteins with high statistical confidence from other tissues suggests that F. grandis may serve as a model fish for future studies of environmental proteomics and ultimately help to elucidate proteomic responses of fish and other vertebrates to environmental stress.
For almost a century, biologists have used trait scaling relationships (bi-variate scatter-plots of trait size versus body size) to characterize phenotypic variation within populations, and to compare animal shape across populations or species.
Scaling relationships are a popular metric because they have long been thought to reflect underlying patterns of trait growth
and development. However, the physiological mechanisms generating animal scaling are not well understood, and it is not yet
clear how scaling relationships evolve. Here we review recent advances in developmental biology, genetics, and physiology
as they pertain to the control of growth of adult body parts in insects. We summarize four mechanisms known to influence either
the rate or the duration of cell proliferation within developing structures, and suggest how mutations in these mechanisms
could affect the relative sizes of adult body parts. By reviewing what is known about these four processes, and illustrating
how they may contribute to patterns of trait scaling, we reveal genetic mechanisms likely to be involved in the evolution
of insect form.
The development of an organism consists of processes occurring in space and time. To analyze this 4-dimensional development in embryogenesis, an appropriate method should be chosen. We present here a sophisticated method, 4D microscopy (3D time-lapse microscopy), initially developed to analyze the cell lineage of wild-type and mutant embryos of the nematode Caenorhabditis elegans. Our method records the entire development of an embryo and allows detailed analyses of events such as cleavage, cell migration, cell death (apoptosis), and cell differentiation during development. The 4D microscopy system has 3 main parts: a motorized microscope, trigger software, and a database that facilitates the analysis of recordings. Adopting the 4D microscopy technique for uses beyond the analysis of C. elegans makes it possible to discern the cell lineage of other small embryos. Our method fills a gap in the study of the development of diverse organisms that are impossible to observe with fluorescent labeling techniques using single blastomeres. The use of this technique to investigate the development of organisms such as tardigrades, acoelomorphs, rotifers, and gastrotrichs provides fresh insight into the evolution of developmental processes and the phylogenetic relationships between such taxa. Using tardigrade development as an example, we demonstrate that the use of 4D microscopy can reveal new characters and corroborate or disapprove old characters. We discuss the results in the light of recent phylogenetic hypotheses regarding the Arthropoda and their probable sister group, the Cycloneuralia, which together form the Ecdysozoa.
In the past decade, there has been a resurgent interest in whether and how phenotypic plasticity might impact evolutionary processes. Of fundamental importance is how the environment influences individual phenotypic development while simultaneously selecting among phenotypic variants in a population. Conceptual and theoretical treatments of the evolutionary implications of plasticity are numerous, as are criticisms of the conclusions. As such, the time is ripe for empirical evidence to catch up with theoretical predictions. To this end, I provide a summary of eight hypotheses at the core of this issue, highlighting various approaches by which they can be tested. My goal is to provide practical guidance to those seeking to understand the complex ways by which phenotypic plasticity can influence evolutionary innovation and diversification.
Bering Sea snow crabs (Chionoecetes opilio) are a commercially important crab harvested in the Bering Sea. Optimal management of this species requires an understanding of the biology of this crab that is currently incomplete. Fisheries managers apply a continuous growth model in their management of snow crab, which assumes that male crabs increase in size throughout their lifespan. Male snow crabs undergo a morphometric molt that leads to a disproportionate increase in chelae size and it is still debated whether this molt is associated with a terminal molt. This study was conducted to determine whether adult male C. opilio are anecdysic. Using current knowledge of the hormonal regulation of crustacean growth, snow crab physiology was manipulated to induce an increase in molting hormones (ecdysteroids). Since female snow crabs are known to undergo a terminal molt after attaining reproductive maturity, we compared ecdysteroid levels in eyestalk-ablated terminally molted females, small-clawed males and large-clawed males. Snow crabs were collected from the Bering Sea and maintained in circulating seawater at approximately 6°C. Animals were either eyestalk-ablated or left intact. Ecdysteroid levels in hemolymph were quantified using an enzyme-linked immunosorbant assay (ELISA). Circulating ecdysteroids were significantly higher in small-clawed male crabs when compared to large-clawed males or terminally molted females. Eyestalk-ablation increased circulating ecdysteroids in small-clawed males, but had no significant effect on circulating ecdysteroids in large-clawed males or in terminally molted females.
Animals have to coordinate a large number of muscles in different ways to efficiently move at various speeds and in different and complex environments. This coordination is in large part based on central pattern generators (CPGs). These neural networks are capable of producing complex rhythmic patterns when activated and modulated by relatively simple control signals. Although the generation of particular gaits by CPGs has been successfully modeled at many levels of abstraction, the principles underlying the generation and selection of a diversity of patterns of coordination in a single neural network are still not well understood. The present work specifically addresses the flexibility of the spinal locomotor networks in salamanders. We compare an abstract oscillator model and a CPG network composed of integrate-and-fire neurons, according to their ability to account for different axial patterns of coordination, and in particular the transition in gait between swimming and stepping modes. The topology of the network is inspired by models of the lamprey CPG, complemented by additions based on experimental data from isolated spinal cords of salamanders. Oscillatory centers of the limbs are included in a way that preserves the flexibility of the axial network. Similarly to the selection of forward and backward swimming in lamprey models via different excitation to the first axial segment, we can account for the modification of the axial coordination pattern between swimming and forward stepping on land in the salamander model, via different uncoupled frequencies in limb versus axial oscillators (for the same level of excitation). These results transfer partially to a more realistic model based on formal spiking neurons, and we discuss the difference between the abstract oscillator model and the model built with formal spiking neurons.
A single tantulus larva was found at the abyssal depth of the Indian Ocean attached to a harpacticoid host of the family Cletodidae.
It represents a new genus and species of Tantulocarida, family Basipodellidae. Its ultrastructure was studied with SEM. This
genus can be easily distinguished from the other genera of Basipodellidae by the pore pattern, bilobed oral disk with strong
longitudinal ridges and the posterior projection of the cephalic shield. A morphological analysis of two related families
Basipodellidae and Deothertridae shows that they represent polyphyletic taxa and need further revision.
The study of parasite evolution relies on the identification of free-living sister taxa of parasitic lineages. Most lineages of parasitic helminths are characterized by an amazing diversity of species that complicates the resolution of phylogenetic relationships. Acanthocephalans offer a potential model system to test various long-standing hypotheses and generalizations regarding the evolution of parasitism in metazoans. The entirely parasitic Acanthocephala have a diversity of species that is manageable with regards to constructing global phylogenetic hypotheses, exhibit variation in hosts and habitats, and are hypothesized to have close phylogenetic affinities to the predominately free-living Rotifera. In this paper, I review and test previous hypotheses of acanthocephalan phylogenetic relationships with analyses of the available 18S rRNA sequence database. Maximum-parsimony and maximum-likelihood inferred trees differ significantly with regard to relationships among acanthocephalans and rotifers. Maximum-parsimony analysis results in a paraphyletic Rotifera, placing a long-branched bdelloid rotifer as the sister taxon of Acanthocephala. Maximum-likelihood analysis results in a monophyletic Rotifera. The difference between the two optimality criteria is attributed to long-branch attraction. The two analyses are congruent in terms of relationships within Acanthocephala. The three sampled classes are monophyletic, and the Archiacanthocephala is the sister taxon of a Palaeacanthocephala + Eoacanthocephala clade. The phylogenetic hypothesis is used to assess the evolution of host and habitat preferences. Acanthocephalan lineages have exhibited multiple radiations into terrestrial habitats and bird and mammal definitive hosts from ancestral aquatic habitats and fish definitive hosts, while exhibiting phylogenetic conservatism in the type of arthropod intermediate host utilized.
The use of fossils in the phylogenetics of extant clades traditionally has been a contentious issue. Fossils usually are relatively incomplete, and their use commonly leads to an increase in the number of equally most parsimonious trees and a decrease in the resolution of phylogenies. Fossils alone, however, provide certain kinds of information about the biological history of a clade, and computer simulations have shown that even highly incomplete material can, under certain circumstances, increase the accuracy of a phylogeny, rather than decrease it.
Because empirical data are still scarce on the effects of the inclusion of fossils on phylogenetic reconstructions, we attempted to investigate this problem by using a relatively well-known group of acanthomorph fishes, the Tetraodontiformes (triggerfishes, pufferfishes, and ocean sunfishes), for which robust phylogenies using extant taxa already exist and that has a well-studied fossil record. Adding incomplete fossil taxa of tetraodontiforms usually increases the number of equally most parsimonious trees and often decreases the resolution of consensus trees. However, adding fossil taxa may help to correctly establish relationships among lineages that have experienced high degrees of morphological diversification by allowing for a reinterpretation of homologous and homoplastic features, increasing the resolution rather than decreasing it. Furthermore, taxa that were scored for 25% or more of their characters did not cause a significant loss of resolution, while providing unique biological information.
The pteropod mollusk Clione limacina swims by dorsal-ventral flapping movements of its wing-like parapodia. Two basic swim speeds are observed—slow and fast.
Serotonin enhances swimming speed by increasing the frequency of wing movements. It does this by modulating intrinsic properties
of swim interneurons comprising the swim central pattern generator (CPG). Here we examine some of the ionic currents that
mediate changes in the intrinsic properties of swim interneurons to increase swimming speed in Clione. Serotonin influences three intrinsic properties of swim interneurons during the transition from slow to fast swimming: baseline
depolarization, postinhibitory rebound (PIR), and spike narrowing. Current clamp experiments suggest that neither Ih nor IA exclusively accounts for the serotonin-induced baseline depolarization. However, Ih and IA both have a strong influence on the timing of PIR—blocking Ih increases the latency to PIR while blocking IA decreases the latency to PIR. Finally, apamin a blocker of IK(Ca) reverses serotonin-induced spike narrowing. These results suggest that serotonin may simultaneously enhance Ih and IK(Ca) and suppress IA to contribute to increases in locomotor speed.
One demand placed exclusively on the musculoskeletal system of females is maintaining locomotor performance with an increasing
load over the reproductive cycle. Here, we examine whether gravid (i.e., “pregnant”) iguanas can increase their force and
power production to support, stabilize, and accelerate the additional mass of a clutch of eggs. At any acceleration, gravid
iguanas produced very high mechanical power (average total power = 673 w/kg; total peak power = 1175 w/kg). While the increase
in total power was partly a result of greater propulsive power (average propulsive power = 25% higher, peak propulsive power = 38%
higher), increased vertical power (roughly 200% increase) was the main contributor. Gravid iguanas were also able to increase
peak forces (propulsive = 23%, mediolateral = 44%, vertical = 42%), and step duration (44%) resulting in greater impulses
(i.e., the sum of force produced during a step) to accelerate, balance, and support their increased mass. The increase in
step duration and smaller increase in peak propulsive force suggests that gravid iguanas may be force-limited in the direction
of motion. We discuss how biomechanical constraints due to females’ reproductive role may influence the evolution of the female
musculoskeletal systems and contribute to the evolution and maintenance of ecological dimorphism in lizards.
Important drivers for emergence of infectious disease in wildlife include changes in the environment, shrinking habitats or
concentration of wildlife, and movement of people, animals, pathogens, or vectors. In this paper we present three case-studies
of emerging parasitic infections and diseases in ungulates in the Canadian north. First we discuss climate warming as an important
driver for the emergence of disease associated with Umingmakstrongylus pallikuukensis, a nematode lungworm of muskoxen. Then we examine how Protostrongylus stilesi, the sheep lungworm, emerged (or re-emerged) in muskoxen after re-introduction of this host into its historical range made
it sympatric with Dall's sheep. Finally, we consider Teladorsagia boreoarcticus, a newly described and common abomasal nematode of muskoxen that is emerging as a disease-causing parasite and may be an
important regulator for muskox populations on Banks Island, Northwest Territories. These and other arctic host-parasite systems
are exquisitely tuned and constrained by a harsh and highly seasonal environment. The dynamics of these systems will be impacted
by climate change and other ecological disruptions. Baseline knowledge of parasite biodiversity and parasite and host ecology,
together with predictive models and long-term monitoring programs, are essential for anticipating and detecting altered patterns
of host range, geographic distribution, and the emergence of parasitic infections and diseases.
Populations of the snow crab (Chionoecetes opilio) are widely distributed on high-latitude continental shelves of the North Pacific and North Atlantic, and represent a valuable resource in both the United States and Canada. In US waters, snow crabs are found throughout the Arctic and sub-Arctic seas surrounding Alaska, north of the Aleutian Islands, yet commercial harvest currently focuses on the more southerly population in the Bering Sea. Population dynamics are well-monitored in exploited areas, but few data exist for populations further north where climate trends in the Arctic appear to be affecting species' distributions and community structure on multiple trophic levels. Moreover, increased shipping traffic, as well as fisheries and petroleum resource development, may add additional pressures in northern portions of the range as seasonal ice cover continues to decline. In the face of these pressures, we examined the ecological niche and population distribution of snow crabs in Alaskan waters using a GIS-based spatial modeling approach. We present the first quantitative open-access model predictions of snow-crab distribution, abundance, and biomass in the Chukchi and Beaufort Seas. Multi-variate analysis of environmental drivers of species' distribution and community structure commonly rely on multiple linear regression methods. The spatial modeling approach employed here improves upon linear regression methods in allowing for exploration of nonlinear relationships and interactions between variables. Three machine-learning algorithms were used to evaluate relationships between snow-crab distribution and environmental parameters, including TreeNet, Random Forests, and MARS. An ensemble model was then generated by combining output from these three models to generate consensus predictions for presence-absence, abundance, and biomass of snow crabs. Each algorithm identified a suite of variables most important in predicting snow-crab distribution, including nutrient and chlorophyll-a concentrations in overlying waters, temperature, salinity, and annual sea-ice cover; this information may be used to develop and test hypotheses regarding the ecology of this species. This is the first such quantitative model for snow crabs, and all GIS-data layers compiled for this project are freely available from the authors, upon request, for public use and improvement.
Phenotypic flexibility in shorebirds has been studied mainly in the context of adjustments to migration and to quality of food; little is known on how birds adjust their phenotype to harsh winter conditions. We showed earlier that red knot (Calidris canutus islandica) can acclimate to cold by elevating body mass. This goes together with larger pectoral muscles, i.e., greater shivering machinery, and thus, better thermogenic capacity. Here, we present results of a yearlong experiment with indoor captive knots to determine whether this strategy is part of their natural seasonal phenotypic cycle. We maintained birds under three thermal regimes: constant cold (5 °C), constant thermoneutrality (25 °C) and natural seasonal variation between these extremes (9-22 °C). Each month we measured variables related to the birds' endurance to cold and physiological maintenance [body mass, thickness of pectoral muscles, summit metabolic rate (M(sum)), food intake, gizzard size, basal metabolic rate (BMR)]. Birds from all treatments expressed synchronized and comparable variation in body mass in spite of thermal treatments, with a 17-18% increase between the warmest and coldest months of the year; which appeared regulated by an endogenous driver. In addition, birds living in the cold exhibited a 10% higher average body mass than did those maintained at thermoneutrality. Thickness of the pectoral muscle tracked changes in body mass in all treatments and likely contributed to greater capacity for shivering in heavier birds. Consequently, M(sum) was 13% higher in cold-acclimated birds compared to those experiencing no thermoregulation costs. However, our data also suggest that part of maximal heat production comes from nonshivering processes. Birds facing cold conditions ate up to 25% more food than did birds under thermoneutral conditions, yet did not develop larger gizzards. Seasonal variation in BMR followed changes in body mass, probably reflecting changes in mass of metabolically active tissues. Just as cold-exposed birds, red knots in the variable treatment increased body mass in winter, thereby improving cold endurance. During summer, however, they maintained a lower body mass and thermogenic capacity compared to cold-exposed birds, similar to individuals kept at thermoneutrality. We conclude that red knots acclimate to seasonal variations in ambient temperature by modulating body mass, combining a preprogrammed increase in mass during winter with a capacity for fine-tuning body mass and thermogenic capacity to temperature variations.
The morphology-performance-fitness paradigm is usually explored by determining whether natural or "phenotypically engineered" variation among individuals in morphology (physiology) or performance covaries with an index of fitness such as survival. Here we study between-line covariation between performance and fitness for 44 lines of flies that had undergone mutation accumulation (in the absence of natural selection) on the second chromosome for 62 generations, plus 13 control lines. These mutation accumulation (MA) lines were known to have reduced competitive fitness and life history scores, and to have positive between-line covariances among life history traits. We measured several performance traits of larvae and adults (and a life history trait), examined covariances among those trait means, and also examined covariances of traits with competitive fitness. MA lines had significantly lower performances than did control lines in most traits. However, because control lines had been unknowingly contaminated, a conclusion that MA reduces performance must be tentative. Correlations among performance traits were highly variable in sign, suggesting that MA does not negatively affect all traits equivalently. Even so, correlation matrices for MA and for control lines were very similar. In bivariate comparisons, only one performance trait (a "get-a-grip index," which measures the ability of a falling fly to catch itself on baffles) was positively correlated with competitive fitness. Multivariate analyses again suggested the importance primarily of get-a-grip. Two main patterns emerge from this study. First, MA negatively affects diverse aspects of physiological performance, but does so differentially across traits. Second, except for GAG, MA-induced variation in performance is at best weakly correlated with competitive fitness.
Benthic marine invertebrates live in a multistressor world where stressor levels are, and will continue to be, exacerbated by global warming and increased atmospheric carbon dioxide. These changes are causing the oceans to warm, decrease in pH, become hypercapnic, and to become less saturated in carbonate minerals. These stressors have strong impacts on biological processes, but little is known about their combined effects on the development of marine invertebrates. Increasing temperature has a stimulatory effect on development, whereas hypercapnia can depress developmental processes. The pH, pCO2, and CaCO3 of seawater change simultaneously with temperature, challenging our ability to predict future outcomes for marine biota. The need to consider both warming and acidification is reflected in the recent increase in cross-factorial studies of the effects of these stressors on development of marine invertebrates. The outcomes and trends in these studies are synthesized here. Based on this compilation, significant additive or antagonistic effects of warming and acidification of the ocean are common (16 of 20 species studied), and synergistic negative effects also are reported. Fertilization can be robust to near-future warming and acidification, depending on the male-female mating pair. Although larvae and juveniles of some species tolerate near-future levels of warming and acidification (+2°C/pH 7.8), projected far-future conditions (ca. ≥4°C/ ≤pH 7.6) are widely deleterious, with a reduction in the size and survival of larvae. It appears that larvae that calcify are sensitive both to warming and acidification, whereas those that do not calcify are more sensitive to warming. Different sensitivities of life-history stages and species have implications for persistence and community function in a changing ocean. Some species are more resilient than others and may be potential "winners" in the climate-change stakes. As the ocean will change more gradually over coming decades than in "future shock" perturbation investigations, it is likely that some species, particularly those with short generation times, may be able to tolerate near-future oceanic change through acclimatization and/or adaption.
More than 100 years ago, Max Rubner combined the fact that both metabolic rate and longevity of mammals varies with body size to calculate that "life energy potential" (lifetime energy turnover per kilogram) was relatively constant. This calculation linked longevity to aerobic metabolism which in turn led to the "rate-of-living" and ultimately the "oxidative stress" theories of aging. However, the link between metabolic rate and longevity is imperfect. Although unknown in Rubner's time, one aspect of body composition of mammals also varies with body size, namely the fatty acid composition of membranes. Fatty acids vary dramatically in their susceptibility to peroxidation and the products of lipid peroxidation are very powerful reactive molecules that damage other cellular molecules. The "membrane pacemaker" modification of the "oxidative stress" theory of aging proposes that fatty acid composition of membranes, via its influence on peroxidation of lipids, is an important determinant of lifespan (and a link between metabolism and longevity). The relationship between membrane fatty acid composition and longevity is discussed for (1) mammals of different body size, (2) birds of different body size, (3) mammals and birds that are exceptionally long-living for their size, (4) strains of mice that vary in longevity, (5) calorie-restriction extension of longevity in rodents, (6) differences in longevity between queen and worker honeybees, and (7) variation in longevity among humans. Most of these comparisons support an important role for membrane fatty acid composition in the determination of longevity. It is apparent that membrane composition is regulated for each species. Provided the diet is not deficient in polyunsaturated fat, it has minimal influence on a species' membrane fatty acid composition and likely also on it's maximum longevity. The exceptional longevity of Homo sapiens combined with the limited knowledge of the fatty acid composition of human tissues support the potential importance of mitochondrial membranes in determination of longevity.
Morphological features of the Acoela appear to be quite plastic, including those of the copulatory organs, which provide the
principle characteristics used for the systematics of this group. Consequently, classification schemes of the Acoela comprise
numerous polyphyletic groupings. In this review, we detail recent revisions of acoel systematics using molecular sequence
data and new and reevaluated morphological characteristics. Gene trees are discordant with traditional systematic schemes
but strongly concordant with new morphological characteristics obtained through the use of transmission electron microscopy
and confocal laser scanning microscopy, namely, characteristics of body-wall and copulatory organ musculature, sperm, sperm
ducts, sagittocysts, and immunocytochemistry of the nervous system. This merger of molecular and morphological data has led
to significant changes in acoel classification, including a major emendation of the largest family of the Acoela, the Convolutidae,
whereby half of its members were transferred to a newly created family, the Isodiametridae.
Different allozyme genotypes at the mannose phosphate isomerase (Mpi) locus in the northern acorn barnacle (Semibalanus balanoides) show a strong association with distinct intertidal microhabitats. In estuaries along the Maine Coast, the FF homozygote has higher fitness in exposed, high-tide level microhabitats while the SS homozygote has higher fitness under algal cover or at low-tide microhabitats. These patterns are consistent with a Levene (1953) model of balancing selection. In these same samples, polymorphisms at the glucose phosphate isomerase locus (Gpi) and mitochondrial DNA (mtDNA) show no fitness differences among microhabitats, providing intra-genomic controls supporting selection at or near Mpi. Here we report a similar analysis of genotype-by-microhabitat associations at sites in Narragansett Bay, Rhode Island, close to the southern range limit of S. balanoides. Genotype zonation at Mpi between high- and low-tide microhabitats is significantly different between Maine and Narragansett Bay due to opposite zonation patterns for the SF and FF genotypes. Enzyme activity data are consistent with this "reverse" zonation. At Gpi, there is significant microhabitat zonation in Narragansett Bay, while this locus behaves as a neutral marker in Maine. Mt DNA shows no significant microhabitat zonation in either Rhode Island or Maine. The Mpi data suggest that Levene-type selection for alternative genotypes in alternative habitats may operate at scales of both 10's of meters and 100's of kilometers. The Gpi data show how an apparently neutral locus can exhibit non-neutral variation under different environmental conditions. We argue that both Mpi and Gpi provide important genetic variation for adaptation to environmental heterogeneity that is recruited under distinct conditions of stress and carbohydrate substrate availability.
Understanding the patterns of genetic variation within and among populations is a central problem in population and evolutionary genetics. We examine this question in the acorn barnacle, Semibalanus balanoides, in which the allozyme loci Mpi and Gpi have been implicated in balancing selection due to varying selective pressures at different spatial scales. We review the patterns of genetic variation at the Mpi locus, compare this to levels of population differentiation at mtDNA and microsatellites, and place these data in the context of genome-wide variation from high-throughput sequencing of population samples spanning the North Atlantic. Despite considerable geographic variation in the patterns of selection at the Mpi allozyme, this locus shows rather low levels of population differentiation at ecological and trans-oceanic scales (F(ST) ~ 5%). Pooled population sequencing was performed on samples from Rhode Island (RI), Maine (ME), and Southwold, England (UK). Analysis of more than 650 million reads identified approximately 335,000 high-quality SNPs in 19 million base pairs of the S. balanoides genome. Much variation is shared across the Atlantic, but there are significant examples of strong population differentiation among samples from RI, ME, and UK. An F(ST) outlier screen of more than 22,000 contigs provided a genome-wide context for interpretation of earlier studies on allozymes, mtDNA, and microsatellites. F(ST) values for allozymes, mtDNA and microsatellites are close to the genome-wide average for random SNPs, with the exception of the trans-Atlantic F(ST) for mtDNA. The majority of F(ST) outliers were unique between individual pairs of populations, but some genes show shared patterns of excess differentiation. These data indicate that gene flow is high, that selection is strong on a subset of genes, and that a variety of genes are experiencing diversifying selection at large spatial scales. This survey of polymorphism in S. balanoides provides a number of genomic tools that promise to make this a powerful model for ecological genomics of the rocky intertidal.
Circulating hormone levels can mediate changes in the quality of courtship signals by males and/or mate choice by females and may thus play an important role in the evolution of courtship signals. Costs associated with shifts in hormone levels of males, for example, could effectively stabilize directional selection by females on male signals. Alternatively, if hormone levels affect the selection of mates by females, then variation in hormone levels among females could contribute to the maintenance of variability in the quality of males' signals. Here, I review what is known regarding the effects of hormone levels on the quality of acoustic signals produced by males and on the choice of mates by females in anuran amphibians. Surprisingly, despite the long history of anuran amphibians as model organisms for studying acoustic communication and physiology, we know very little about how variation in circulating hormone levels contributes to variation in the vocal quality of males. Proposed relationships between androgen levels and vocal quality depicted in recent models, for example, are subject to the same criticisms raised for similar models proposed in relation to birds, namely that the evidence for graded effects of androgens on vocal performance is often weak or not rigorously tested and responses seen in one species are often not observed in other species. Although several studies offer intriguing support for graded effects of hormones on calling behavior, additional comparative studies will be required to understand these relationships. Recent studies indicate that hormones may also mediate changes in anuran females' choice of mates, suggesting that the hormone levels of females can influence the evolution of males' mating signals. No studies to date have concurrently addressed the potential complexity of hormone-behavior relationships from the perspective of sender as well as receiver, nor have any studies addressed the costs that are potentially associated with changes in circulating hormone levels in anurans (i.e., life-history tradeoffs associated with elevations in circulating androgens in males). The mechanisms involved in hormonally induced changes in signal production and selectivity also require further investigation. Anuran amphibians are, in many ways, conducive to investigating such questions.
Successful reproduction requires contributions from both the male and the female. In Drosophila, contributions from the male include accessory gland proteins (Acps) that are components of the seminal fluid. Upon their transfer to the female, Acps affect the female's physiology and behavior. Although primary sequences of Acp genes exhibit variation among species and genera, the conservation of protein biochemical classes in the seminal fluid suggests a conservation of functions. Bioinformatics coupled with molecular and genetic tools available for Drosophila melanogaster has expanded the functional analysis of Acps in recent years to the genomic/proteomic scale. Molecular interplay between Acps and the female enhances her egg production, reduces her receptivity to remating, alters her immune response and feeding behavior, facilitates storage and utilization of sperm in the female and affects her longevity. Here, we provide an overview of the D. melanogaster Acps and integrate the results from several studies that bring the current number of known D. melanogaster Acps to 112. We then discuss several examples of how the female's physiological processes and behaviors are mediated by interactions between Acps and the female. Understanding how Acps elicit particular female responses will provide insights into reproductive biology and chemical communication, tools for analyzing models of sexual cooperation and/or sexual conflict, and information potentially useful for strategies for managing insect pests.
We studied the occurrence of torpor in golden spiny mice in a hot rocky desert near the Dead Sea. In this rodent assemblage, a congener, the nocturnal common spiny mouse, competitively excluded the golden spiny mouse from the nocturnal part of the diel cycle and forced it into diurnal activity; this temporal partitioning allows the two species to partition their prey populations, particularly in summer when the diet of the two species is comprised mainly of arthropods, and largely overlap. We studied the effect of the presence of the common spiny mice at two resource levels (natural food availability and food added ad libitum) on populations of golden spiny mice in four large outdoor enclosures: two with common spiny mice removed and two enclosures with populations of both species. We hypothesized that with interspecific competition and/or reduced resources, golden spiny mice will increase their use of torpor. As we expected, supplemented food reduced the total time spent torpid. In summer, when the different activity periods of the two species results in prey species partitioning, removal of the congener did not affect torpor in the golden spiny mouse. However, in winter, when insect populations are low and the two species of mice overlap in a largely vegetarian diet, removal of the common spiny mouse reduced torpor in golden spiny mice, whether food was supplemented or not. This result suggests that torpor, a mechanism that allows small mammals to sustain periods of low availability of resources or high energetic requirements, may also help them to tolerate periods of enhanced interspecific competition. This may be a significant short-term mechanism that reduces competition and hence increases fitness, in particular of individuals of the subordinate species whose accessibility to resources may be limited.
The establishment of a publicly-accessible repository of physiological data on feeding in mammals, the Feeding Experiments End-user Database (FEED), along with improvements in reconstruction of mammalian phylogeny, significantly improves our ability to address long-standing questions about the evolution of mammalian feeding. In this study, we use comparative phylogenetic methods to examine correlations between jaw robusticity and both the relative recruitment and the relative time of peak activity for the superficial masseter, deep masseter, and temporalis muscles across 19 mammalian species from six orders. We find little evidence for a relationship between jaw robusticity and electromyographic (EMG) activity for either the superficial masseter or temporalis muscles across mammals. We hypothesize that future analyses may identify significant associations between these physiological and morphological variables within subgroups of mammals that share similar diets, feeding behaviors, and/or phylogenetic histories. Alternatively, the relative peak recruitment and timing of the balancing-side (i.e., non-chewing-side) deep masseter muscle (BDM) is significantly negatively correlated with the relative area of the mandibular symphysis across our mammalian sample. This relationship exists despite BDM activity being associated with different loading regimes in the symphyses of primates compared to ungulates, suggesting a basic association between magnitude of symphyseal loads and symphyseal area among these mammals. Because our sample primarily represents mammals that use significant transverse movements during chewing, future research should address whether the correlations between BDM activity and symphyseal morphology characterize all mammals or should be restricted to this "transverse chewing" group. Finally, the significant correlations observed in this study suggest that physiological parameters are an integrated and evolving component of feeding across mammals.
The last common ancestor of extant bilaterian animals is often referred to as “Urbilateria”. Comparative studies of development
in a variety of laboratory animals, both traditional model systems and newer “emerging” models, have resulted in many proposals
as to the morphological and developmental genetic characteristics of Urbilateria. Most of these proposals are concerned with
the development and emergence of external morphology, such as appendages, eyes, and ectodermal segmentation. Less attention
has been paid to the evolutionary developmental biology of organogenesis. Arguably, one of the most important aspects of urbilaterian
organogenesis would have been gonadogenesis, since Urbilateria must have successfully generated gametes and developed a strategy
for extrusion and fertilization, in order to be the ancestor of all living Bilateria. This article considers what is known
about gonadogenesis and reproductive strategies in extant metazoans, and searches for phylogenetic patterns that suggest what
shared characteristics of these processes Urbilateria might have displayed. I conclude that the data presently available cannot
suggest homologies of the somatic components of metazoan gonads, and that convergent evolution has resulted in many different
morphological, and possibly molecular genetic, solutions to the various problems posed by sexual reproduction.
Gradients of air temperature, radiation, and other climatic factors change systematically but differently with altitude and latitude. We explore how these factors combine to produce altitudinal and latitudinal patterns of body temperature, thermal stress, and seasonal overlap that differ markedly from patterns based solely on air temperature. We use biophysical models to estimate body temperature as a function of an organism's phenotype and environmental conditions (air and surface temperatures and radiation). Using grasshoppers as a case study, we compare mean body temperatures and the incidence of thermal extremes along altitudinal gradients both under past and current climates. Organisms at high elevation can experience frequent thermal stress despite generally cooler air temperatures due to high levels of solar radiation. Incidences of thermal stress have increased more rapidly than have increases in mean conditions due to recent climate change. Increases in air temperature have coincided with shifts in cloudiness and solar radiation, which can exacerbate shifts in body temperature. We compare altitudinal thermal gradients and their seasonality between tropical and temperate mountains to ask whether mountain passes pose a greater physiological barrier in the tropics (Janzen's hypothesis). We find that considering body temperature rather than air temperature generally increases the amount of overlap in thermal conditions along gradients in elevation and thus decreases the physiological barrier posed by tropical mountains. Our analysis highlights the limitations of predicting thermal stress based solely on air temperatures, and the importance of considering how phenotypes influence body temperatures.
Little is known about the potential for rapid evolution in natural populations in response to the high rate of contemporary climatic change. Organisms that have evolved in environments that experience high variability across space and time are of particular interest as they may harbor genetic variation that can facilitate evolutionary response to changing conditions. Here we review what is known about genetic capacity for adaptation in the purple sea urchin, Strongylocentrotus purpuratus, a species that has evolved in the upwelling ecosystem of the Northeast Pacific Ocean. We also present new results testing for adaptation to local pH conditions in six populations from Oregon to southern California. We integrate data on 19,493 genetic polymorphisms with data on local pH conditions. We find correlations between allele frequency and rank average time spent at pH <7.8 in 318 single-nucleotide polymorphisms in 275 genes. Two of the genes most correlated with local pH are a protein associated with the cytoskeleton and a proton pump, with functional roles in maintenance of cell volume and with internal regulation of pH, respectively. Across all loci tested, high correlations with local pH were concentrated in genes related to transport of ions, biomineralization, lipid metabolism, and cell-cell adhesion, functional pathways important for maintaining homeostasis at low pH. We identify a set of seven genes as top candidates for rapid evolutionary response to acidification of the ocean. In these genes, the putative low-pH-adapted allele, based on allele frequencies in natural populations, rapidly increases in frequency in purple sea urchin larvae raised at low pH. We also found that populations from localities with high pH show a greater change in allele frequency toward putative low-pH-adapted alleles under experimental acidification, compared with low-pH populations, suggesting that both natural and artificial selection favor the same alleles for response to low pH. These results illustrate that purple sea urchins may be adapted to local pH and suggest that this species may possess the genetic capacity for rapid evolution in response to acidification. This adaptive capacity likely comes from standing genetic variation maintained in nature by balancing selection across the spatial and temporal environmental mosaic that characterizes the California Current Ecosystem.
For marine, benthic animals, duration of planktonic larval stages is expected to correlate with dispersal ability, and thus species ranges, at least where planktonic dispersal is necessary to reach habitats. Yet past analyses of larval duration and species ranges across the insular Pacific show at most a weak correlation. So, do larvae matter in determining species ranges in such an island setting? We analyze an extensive dataset on cowries and find, again, that estimated larval duration does not correlate with species ranges. Several factors can obscure a real correlation, however, including estimation error, intraspecific variation, other factors affecting dispersal, poor taxonomy, and remote endemics. We show that taking these into consideration greatly improves correlation. Further evidence for the importance of larval duration comes from diversity and speciation patterns. Diversity of poor dispersers drops more rapidly eastward across the Pacific and leads to taxonomic differences in community composition across the basin. Geographic scale of differentiation is strongly influenced by larval duration and leads to the most rapid diversification at intermediate dispersal capacities. A major lesson from the phylogenetically corrected cowrie dataset is that without accurate and appropriate taxonomy, clear and important distributional and diversity patterns can become obscured. Inappropriate taxonomic scale can also obscure macroecological patterns: cowrie tribes/subfamilies show substantial variation in the steepness of their diversity cline across the Pacific and in their proportional local abundance, showing the importance of ecological traits in controlling distributions. In contrast such variation was not evident in a study focused at the family level in corals and fishes.
Biologists that study mammals continue to discuss the evolution of and functional variation in jaw-muscle activity during chewing. A major barrier to addressing these issues is collecting sufficient in vivo data to adequately capture neuromuscular variation in a clade. We combine data on jaw-muscle electromyography (EMG) collected during mastication from 14 species of primates and one of treeshrews to assess patterns of neuromuscular variation in primates. All data were collected and analyzed using the same methods. We examine the variance components for EMG parameters using a nested ANOVA design across successive hierarchical factors from chewing cycle through species for eight locations in the masseter and temporalis muscles. Variation in jaw-muscle EMGs was not distributed equally across hierarchical levels. The timing of peak EMG activity showed the largest variance components among chewing cycles. Relative levels of recruitment of jaw muscles showed the largest variance components among chewing sequences and cycles. We attribute variation among chewing cycles to (1) changes in food properties throughout the chewing sequence, (2) variation in bite location, and (3) the multiple ways jaw muscles can produce submaximal bite forces. We hypothesize that variation among chewing sequences is primarily related to variation in properties of food. The significant proportion of variation in EMGs potentially linked to food properties suggests that experimental biologists must pay close attention to foods given to research subjects in laboratory-based studies of feeding. The jaw muscles exhibit markedly different variance components among species suggesting that primate jaw muscles have evolved as distinct functional units. The balancing-side deep masseter (BDM) exhibits the most variation among species. This observation supports previous hypotheses linking variation in the timing and activation of the BDM to symphyseal fusion in anthropoid primates and in strepsirrhines with robust symphyses. The working-side anterior temporalis shows a contrasting pattern with little variation in timing and relative activation across primates. The consistent recruitment of this muscle suggests that primates have maintained their ability to produce vertical jaw movements and force in contrast to the evolutionary changes in transverse occlusal forces driven by the varying patterns of activation in the BDM.
Fish inhabit environments greatly varying in intensity of water velocity, and these flow regimes are generally believed to be of major evolutionary significance. To what extent does water flow drive repeatable and predictable phenotypic differentiation? Although many investigators have examined phenotypic variation across flow gradients in fishes, no clear consensus regarding the nature of water velocity's effects on phenotypic diversity has yet emerged. Here, I describe a generalized model that produces testable hypotheses of morphological and locomotor differentiation between flow regimes in fishes. The model combines biomechanical information (describing how fish morphology determines locomotor abilities) with ecological information (describing how locomotor performance influences fitness) to yield predictions of divergent natural selection and phenotypic differentiation between low-flow and high-flow environments. To test the model's predictions of phenotypic differentiation, I synthesized the existing literature and conducted a meta-analysis. Based on results gathered from 80 studies, providing 115 tests of predictions, the model produced some accurate results across both intraspecific and interspecific scales, as differences in body shape, caudal fin shape, and steady-swimming performance strongly matched predictions. These results suggest that water flow drives predictable phenotypic variation in disparate groups of fish based on a common, generalized model, and that microevolutionary processes might often scale up to generate broader, interspecific patterns. However, too few studies have examined differentiation in body stiffness, muscle architecture, or unsteady-swimming performance to draw clear conclusions for those traits. The analysis revealed that, at the intraspecific scale, both genetic divergence and phenotypic plasticity play important roles in phenotypic differentiation across flow regimes, but we do not yet know the relative importance of these two sources of phenotypic variation. Moreover, while major patterns within and between species were predictable, we have little direct evidence regarding the role of water flow in driving speciation or generating broad, macroevolutionary patterns, as too few studies have addressed these topics or conducted analyses within a phylogenetic framework. Thus, flow regime does indeed drive some predictable phenotypic outcomes, but many questions remain unanswered. This study establishes a general model for predicting phenotypic differentiation across flow regimes in fishes, and should help guide future studies in fruitful directions, thereby enhancing our understanding of the predictability of phenotypic variation in nature.
Most animals begin life in eggs, protected and constrained by a capsule, shell, or other barrier. As embryos develop, their needs and abilities change, altering the costs and benefits of encapsulation, and the risks and opportunities of the outside world. When the cost/benefit ratio is better outside the egg, animals should hatch. Adaptive timing of hatching evolves in this context. However, many environmental variables affect the optimal timing of hatching so there is often no consistent best time. Across a broad range of animals, from flatworms and snails to frogs and birds, embryos hatch at different times or at different developmental stages in response to changing risks or opportunities. Embryos respond to many types of cues, assessed via different sensory modalities. Some responses appear simple. Others are surprisingly complex and sophisticated. Parents also manipulate the timing of hatching. The number and breadth of examples of cued hatching suggest that, in the absence of specific information, we should not assume that hatching timing is fixed. Our challenge now is to integrate information on the timing of hatching across taxa to better understand the diversity of patterns and how they are structured in relation to different types of environmental and developmental variation. As starting points for comparative studies, I: (1) suggest a framework based on heterokairy-individual, plastic variation in the rate, timing, or sequence of developmental events and processes-to describe patterns and mechanisms of variation in the timing of hatching; (2) briefly review the distribution of environmentally cued hatching across the three major clades of Bilateria, highlighting the diverse environmental factors and mechanisms involved; and (3) discuss factors that shape the diversity of plastic and fixed timing of hatching, drawing on evolutionary theory on phenotypic plasticity which directs our attention to fitness trade-offs, environmental heterogeneity, and predictive cues. Combining mechanistic and evolutionary perspectives is necessary because development changes organismal interactions with the environment. Integrative and comparative studies of the timing of hatching will improve our understanding of embryos as both evolving and developing organisms.