How functional is functional? Ecological groupings in terrestrial animal ecology: towards an animal functional type approach

Understanding mechanisms to predict changes in plant and animal communities is a key challenge in ecology. The need to transfer knowledge gained from single species to a more generalized approach has led to the development of categorization systems where species’ similarities in life strategies and traits are classified into ecological groups (EGs) like functional groups/types or guilds. While approaches in plant ecology undergo a steady improvement and refinement of methodologies, progression in animal ecology is lagging behind. With this review, we aim to initiate a further development of functional classification systems in animal ecology, comparable to recent developments in plant ecology. We here (i) give an overview of terms and definitions of EGs in animal ecology, (ii) discuss existing classification systems, methods and application areas of EGs (focusing on terrestrial vertebrates), and (iii) provide a “roadmap towards an animal functional type approach” for improving the application of EGs and classifications in animal ecology. We found that an animal functional type approach requires: (i) the identification of core traits describing species’ dependency on their habitat and life history traits, (ii) an optimization of trait selection by clustering traits into hierarchies, (iii) the assessment of “soft traits” as substitute for hardly measurable traits, e.g. body size for dispersal ability, and (iv) testing of delineated groups for validation including experiments.     

Pond tadpoles with generalized morphology: is it time to reconsider their functional roles in aquatic communities?

With rare exceptions, anuran larvae have traditionally been considered to occupy lower trophic levels in aquatic communities where they function as microphagous suspension feeders. This view is being challenged by studies showing that tadpoles with generalized morphology often function as macrophagous predators. Here, we review the literature concerning macrophagy by tadpoles and provide two additional examples involving generalized tadpoles. In the first, we demonstrate with laboratory and field experiments that wood frog (Rana sylvatica) tadpoles are major predators of macroinvertebrates in ponds. In the second, we show that green frog (R. clamitans) tadpoles can cause catastrophic reproductive failure of the wood frog via egg predation. These results and data from other studies challenge the assumption that generalized tadpoles function as filter-feeding omnivores, and question the general applicability of community organization models which assume that predation risk increases with pond permanence. We suggest that predation risk is greater in temporary ponds than in more permanent ponds for many organisms that are vulnerable to predation by tadpoles. This being so, a conditional model based upon interactions that are species-specific, life-stage-specific, and context-dependent may better explain community organization along hydrological gradients than models which assume that temporary ponds have few or no predators. Received: 30 November 1998 / Accepted: 2 May 1999     

Why do animals have so many receptors? The role of multiple chemosensors in animal perception

Many animals have an abundance and diverse assortment of peripheral sensors, both across and within sensory modalities. Multiple sensors offer many functional advantages to an animal's ability to perceive and respond to environmental signals. Advantages include extending the ability to detect and determine the spatial distribution of stimuli, improving the range and accuracy of discrimination among stimuli of different types and intensities, increasing behavioral sensitivity to stimuli, ensuring continued sensory capabilities when the probability of damage or other loss of function to some sensors is high, maintaining sensory function over the entire sensory surface during development and growth, and increasing the richness of behavioral output to sensory stimulation. In this paper, we use the crustacean chemosensory system as the primary example to discuss these functions of multiple sensors. These principles may be applicable to the function of autonomous robots and should be considered in their design.     

The many facets of the Tim-Tipin protein families’ roles in chromosome biology

Failures in DNA replication are a potent force for driving genome instability. The proteins which form the replisome, the DNA replication machinery, play a fundamental role in preventing replicative catastrophes. The Tim (TIMELESS/TIMEOUT) and Tipin proteins are two conserved replisome associated proteins which have functions in preventing replication fork collapse and replicative checkpoint signalling in response to factors which slow the progression of the replisome. Intriguingly, TIMELESS family members have been implicated in the regulation of the biological clock, giving a tantalising pointer to a possible link between DNA replication and circadian rhythm control. Here we report on our current understanding of the many facets of these protein families in maintaining genome stability and replication checkpoint control.     

Inhibitory or excitatory? Optogenetic interrogation of the functional roles of GABAergic interneurons in epileptogenesis

Alteration in the excitatory/inhibitory neuronal balance is believed to be the underlying mechanism of epileptogenesis. Based on this theory, GABAergic interneurons are regarded as the primary inhibitory neurons, whose failure of action permits hyperactivity in the epileptic circuitry. As a consequence, optogenetic excitation of GABAergic interneurons is widely used for seizure suppression. However, recent evidence argues for the context-dependent, possibly “excitatory” roles that GABAergic cells play in epileptic circuitry. We reviewed current optogenetic approaches that target the “inhibitory” roles of GABAergic interneurons for seizure control. We also reviewed interesting evidence that supports the “excitatory” roles of GABAergic interneurons in epileptogenesis. GABAergic interneurons can provide excitatory effects to the epileptic circuits via several distinct neurological mechanisms. (1) GABAergic interneurons can excite postsynaptic neurons, due to the raised reversal potential of GABA receptors in the postsynaptic cells. (2) Continuous activity in GABAergic interneurons could lead to transient GABA depletion, which prevents their inhibitory effect on pyramidal cells. (3) GABAergic interneurons can synchronize network activity during seizure. (4) Some GABAergic interneurons inhibit other interneurons, causing disinhibition of pyramidal neurons and network hyperexcitability. The dynamic, context-dependent role that GABAergic interneurons play in seizure requires further investigation of their functions at single cell and circuitry level. New optogenetic protocols that target GABAergic inhibition should be explored for seizure suppression.     

The use of animal models in the study of complex disease: all else is never equal or why do so many human studies fail to replicate animal findings?

The study of the genetics of complex human disease has met with limited success. Many findings with candidate genes fail to replicate despite seemingly overwhelming physiological data implicating the genes. In contrast, animal model studies of the same genes and disease models usually have more consistent results. We propose that one important reason for this is the ability to control genetic background in animal studies. The fact that controlling genetic background can produce more consistent results suggests that the failure to replicate human findings in the same diseases is due to variation in interacting genes. Hence, the contrasting nature of the findings from the different study designs indicates the importance of non-additive genetic effects on human disease. We discuss these issues and some methodological approaches that can detect multilocus effects, using hypertension as a model disease. This article contains supplementary material, which may be viewed at the BioEssays website at http://www.interscience.wiley.com/jpages/0265-9247/suppmat/index.html.     

The role of trematode parasites in larval anuran communities: an aquatic ecologist’s guide to the major players

Conservation strategies depend on our understanding of the ecosystem and community dynamics. To date, such understanding has focused mostly on predator–prey and competitor interactions. It is increasingly clear, however, that parasite–host interactions may represent a large, and important, component of natural communities. The need to consider multiple factors and their synergistic interactions if we are to elucidate the contribution of anthropogenic factors to loss in biodiversity is exemplified by research into present-day amphibian declines. Only recently has the role of factors such as trematode parasite infections been incorporated into studies of the population and community dynamics of aquatic systems. We argue that this is due, at least in part, to difficulties faced by aquatic ecologists in sifting through the complex systematics that pervade the parasite literature. We note that two trematode species are of dominant importance with regard to North American larval anuran communities, and provide in this review a clear explanation of how to distinguish between the infective stages of these two parasites. We describe the general biology and life history of these parasites, as well as what is known about their effect on larval anurans, and the interactive effects of environmental stressors (typically anthropogenic in nature) and parasites on larval anurans. We hope that this review will convince the reader of the potential importance of these parasites to aquatic communities in general, and to amphibian communities specifically, and will also provide the information necessary for aquatic ecologists to more frequently consider the role of these parasites in their studies of aquatic ecology.     

Santa rosalia revisited: or why are there so many kinds of parasites in ;the garden of earthly delights'?

As is the case for free-living species, a very large number of parasitic species are not described adequately by the biological species concept. Furthermore, Thierry de Mee?s, Yannis Michalakis and Fran?ois Renaud argue that because hosts represent a highly heterogeneous and changing environment as well as a breeding site, favouring the association of host-adaptation and host-choice genes, sympatric speciation may occur frequently in parasitic organisms. Therefore, parasites appear to be ideal biological models for the study of ecological specialization and speciation. Beyond the relevance of such considerations in fundamental science, the study of the origin and evolution of parasite diversity has important implications for more applied fields such as epidemiology and diagnosis.     

The evolution of early animal embryos: conservation or divergence?

There is a remarkable similarity in the appearance of groups of animal species during periods of their embryonic development. This classic observation has long been viewed as an emphatic realization of the principle of common descent. Despite the importance of embryonic conservation as a unifying concept, models seeking to predict and explain different patterns of conservation have remained in contention. Here, we focus on early embryonic development and discuss several lines of evidence, from recent molecular data, through developmental networks to life-history strategies, that indicate that early animal embryos are not highly conserved. Bringing this evidence together, we argue that the nature of early development often reflects adaptation to diverse ecological niches. Finally, we synthesize old and new ideas to propose a model that accounts for the evolutionary process by which embryos have come to be conserved.     

Plant response to disturbance in a Mediterranean grassland: How many functional groups?

Abstract. Data referring to changes in vegetation composition resulting from cattle exclosure and ploughing in a Portuguese pasture dominated by annuals were used to test hypotheses regarding the biology of species favoured or eliminated by disturbance in semi-natural herbaceous communities. These hypotheses were tested in two ways. First we compared the distribution of six a priori groups – grasses, small rosettes, large rosettes, small species with leafy stems, large species with leafy stems, legumes – across grazed, ploughed and undisturbed plots. In a second set of analyses we examined changes in the frequencies of individual biological attributes in response to grazing and ploughing. These analyses were carried out separately for grasses and dicot forbs. Overall, the species composition showed little response to either grazing or ploughing, though species dominance changed. This lack of responsiveness of species composition was attributed to the long history of intensive land use which has resulted in the loss of disturbance-intolerant species over entire landscapes. When considering a priori groups, small rosettes were indifferent to disturbance. grazing and ploughing showed that dominated. Large rosettes, large species with leafy stems and legumes were generally intolerant to both grazing and ploughing, though individual species may increase in response to disturbance. Small species with leafy stems were the only group favoured by grazing whereas ploughing favoured grasses. As to individual traits, grazing excluded large grass species with heavy seeds and promoted a flat rosette canopy structure and a small size, along with a moderate dormancy and protected inflorescences. In forbs, grazing favoured small species, as expected, while it excluded tall species, and, in contrast to earlier results, a rosette canopy. These attributes were consistent with responses of the a priori groups, though it would not have been possible to reconstruct groups directly from the attribute list. Ploughing had no effect on any of the forb traits. As to grass traits, flat- and short-statured species increased and heavy-seeded species decreased. Our analysis revealed two advantages of establishing plant functional classifications within life forms. Subgroups within forbs had contrasting types of behaviour. For the same trait patterns could differ within the grass group from within the forb group. Finally, this analysis emphasizes the need for plant functional classifications aiming at the identification of syndromes of co-occurring attributes rather than of lists of isolated traits of which actual combinations are not specified.     

The VNTR in complex disorders: The forgotten polymorphisms? A functional way forward?

In the last few years, research has focused on single nucleotide polymorphisms (SNPs) in the search for underlying genetic aetiology of complex disorders. This has been afforded by the rapid technological advancement to enable the interrogation of hundreds of thousands of SNPs in one assay via microarrays. However SNPs are only one form of genetic variation and in the midst of the Genome-Wide Association Study (GWAS) explosion Variable Number Tandem Repeat (VNTR) polymorphism exploration has seemingly been left behind. This review will argue that VNTR investigations still hold substantial potential for a role in complex disorders via possible functional properties.     

The species concept in parasites and other pathogens: a pragmatic approach?

Although the problem of speciation is a puzzle for evolutionists, species are not mere fantasies. In many cases, it is possible to identify evolutionary entities that deserve to be attributed the name 'species' and that are relevant to medical researchers and decision makers. All approaches to the problem of speciation in pathogens are specific cases of four main concepts (or combinations thereof): biological, phylogenetic, phenetic and phenotypic. Modern genetic concepts and technologies help to juggle these concepts.