Long-term TE persistence even without beneficial insertion.

This correspondence responds to the critique by Butler et al. (BMC Genomics 22:241, 2021) of our recent paper on transposable element (TE) persistence. We address the three main objections raised by Butler et al. After running a series of additional simulations that were inspired by the authors' criticisms, we are able to present a more nuanced understanding of the conditions that generate long-term persistence.

Transposable element persistence via potential genome-level ecosystem engineering.

BACKGROUND: The nuclear genomes of eukaryotes vary enormously in size, with much of this variability attributable to differential accumulation of transposable elements (TEs). To date, the precise evolutionary and ecological conditions influencing TE accumulation remain poorly understood. Most previous attempts to identify these conditions have focused on evolutionary processes occurring at the host organism level, whereas we explore a TE ecology explanation. RESULTS: As an alternative (or additional) hypothesis, we propose that ecological mechanisms occurring within the host cell may contribute to patterns of TE accumulation. To test this idea, we conducted a series of experiments using a simulated asexual TE/host system. Each experiment tracked the accumulation rate for a given type of TE within a particular host genome. TEs in this system had a net deleterious effect on host fitness, which did not change over the course of experiments. As one might expect, in the majority of experiments TEs were either purged from the genome or drove the host population to extinction. However, in an intriguing handful of cases, TEs co-existed with hosts and accumulated to very large numbers. This tended to occur when TEs achieved a stable density relative to non-TE sequences in the genome (as opposed to reaching any particular absolute number). In our model, the only way to maintain a stable density was for TEs to generate new, inactive copies at a rate that balanced with the production of active (replicating) copies. CONCLUSIONS: From a TE ecology perspective, we suggest this could be interpreted as a case of ecosystem engineering within the genome, where TEs persist by creating their own "habitat".

Ecological laws for agroecological design: the need for more organized collaboration in producing, evaluating and updating ecological generalizations.

The applied discipline of agroecological design provides a useful case study for examining broader philosophical questions about the existence and importance of ecological generalizations or "laws." Recent developments in the availability and use of formal meta-analyses have led to the discovery of many resilient generalizations in ecology (Linquist et al. 2016). However, these "laws" face numerous challenges when it comes to their practical application. Concerns about their reliability and scope might stem from unclear logical and epistemic connections to more foundational or "unifying" generalizations (Lean in Philos Top 47(1), 2019) which, in ecology, tend to be derived from first principles and in association with highly abstract models. This raises questions about the nature of those foundational generalizations themselves. In particular, how resilient are they compared to the generalizations uncovered by empirically driven methods? Here we propose a procedure for evaluating the resilience of generalizations across five ecologically relevant dimensions. This procedure was applied to seven well known foundational generalizations in ecology. Surprisingly, it turned out to be impossible to estimate the resilience of these foundational generalizations based on the available literature. This points to the need for a more centralized repository of information about ecological generalizations, created with the explicit aim of evaluating such important dimensions as causal mechanism and predictive power.

Commitment enforcement also explains shamanism's culturally shared features.

The proposed explanation for the evolution of shamanism is not the only viable option. I sketch an alternative commitment hypothesis that views shamanism as an adaptation at the level of biological individuals or cultural groups. To the extent that these hypotheses make overlapping predictions about the culturally shared features of shamanism, we lack adequate evidence to discriminate among them.

Applying ecological models to communities of genetic elements: the case of neutral theory.

A promising recent development in molecular biology involves viewing the genome as a mini-ecosystem, where genetic elements are compared to organisms and the surrounding cellular and genomic structures are regarded as the local environment. Here, we critically evaluate the prospects of ecological neutral theory (ENT), a popular model in ecology, as it applies at the genomic level. This assessment requires an overview of the controversy surrounding neutral models in community ecology. In particular, we discuss the limitations of using ENT both as an explanation of community dynamics and as a null hypothesis. We then analyse a case study in which ENT has been applied to genomic data. Our central finding is that genetic elements do not conform to the requirements of ENT once its assumptions and limitations are made explicit. We further compare this genome-level application of ENT to two other, more familiar approaches in genomics that rely on neutral mechanisms: Kimura's molecular neutral theory and Lynch's mutational-hazard model. Interestingly, this comparison reveals that there are two distinct concepts of neutrality associated with these models, which we dub 'fitness neutrality' and 'competitive neutrality'. This distinction helps to clarify the various roles for neutral models in genomics, for example in explaining the evolution of genome size.

Conceptual and empirical challenges of ascribing functions to transposable elements.

Media attention and the subsequent scientific backlash engendered by the claim by spokespeople for the Encyclopedia of DNA Elements (ENCODE) project that 80% of the human genome has a biochemical function highlight the need for a clearer understanding of function concepts in biology. This article provides an overview of two major function concepts that have been developed in the philosophy of science--the causal role concept and the selected effects concept--and their relevance to ENCODE. Unlike in some previous critiques, the ENCODE project is not considered problematic here because it employed a causal role definition of function (which is relatively common in genetics) but because of how this concept was misused. In addition, several unique challenges that arise when dealing with transposable elements (TEs) but that were ignored by ENCODE are highlighted. These include issues surrounding TE-level versus organism-level selection, the origins versus the persistence of elements, and accidental versus functional organism-level benefits. Finally, some key questions are presented that should be addressed in any study aiming to ascribe functions to major portions of large eukaryotic genomes, the majorities of which are made up of transposable elements.

A novel application of ecological analyses to assess transposable element distributions in the genome of the domestic cow, Bos taurus.

Transposable elements (TEs) are among the most abundant components of many eukaryotic genomes. Efforts to explain TE abundance, as well as TE diversity among genomes, have led some researchers to draw an analogy between genomic and ecological processes. Adopting this perspective, we conducted an analysis of the cow (Bos taurus) genome using techniques developed by community ecologists to determine whether environmental factors influence community composition. Specifically, each chromosome within the Bos taurus genome was treated as a "linear transect", and a multivariate redundancy analysis (RDA) was used to identify large-scale spatial patterns in TE communities associated with 10 TE families. The position of each TE community on the chromosome accounted for ∼50% of the variation along the chromosome "transect". Multivariate analysis further revealed an effect of gene density on TE communities that is influenced by several other factors in the (genomic) environment, including chromosome length and TE density. The results of this analysis demonstrate that ecological methods can be applied successfully to help answer genomic questions.

In the line of fire: Debris throwing by wild octopuses.

Wild Octopus tetricus frequently propel shells, silt, and algae through the water by releasing these materials from their arms while creating a forceful jet from the siphon held under the arm web. These "throws" occur in several contexts at a site in Jervis Bay, Australia, including in interactions with other octopuses. Material thrown in interactive contexts frequently hits other octopuses. Some throws appear to be targeted on other individuals, as suggested by several kinds of evidence: Throws in interactive contexts were more vigorous than others, and more often used silt, rather than shells or algae. High vigor throws were more often accompanied by uniform or dark body patterns than other throws. Some throws were directed differently from beneath the arms and such throws were more likely to hit other octopuses. Throwing at other individuals in the same population, as apparently seen in these octopuses, is a rare form of nonhuman projectile use, previously seen only in some social mammals.

Transposon dynamics and the epigenetic switch hypothesis.

The recent explosion of interest in epigenetics is often portrayed as the dawning of a scientific revolution that promises to transform biomedical science along with developmental and evolutionary biology. Much of this enthusiasm surrounds what we call the epigenetic switch hypothesis, which regards certain examples of epigenetic inheritance as an adaptive organismal response to environmental change. This interpretation overlooks an alternative explanation in terms of coevolutionary dynamics between parasitic transposons and the host genome. This raises a question about whether epigenetics researchers tend to overlook transposon dynamics more generally. To address this question, we surveyed a large sample of scientific publications on the topics of epigenetics and transposons over the past fifty years. We found that enthusiasm for epigenetics is often inversely related to interest in transposon dynamics across the four disciplines we examined. Most surprising was a declining interest in transposons within biomedical science and cellular and molecular biology over the past two decades. Also notable was a delayed and relatively muted enthusiasm for epigenetics within evolutionary biology. An analysis of scientific abstracts from the past twenty-five years further reveals systematic differences among disciplines in their uses of the term epigenetic, especially with respect to heritability commitments and functional interpretations. Taken together, these results paint a nuanced picture of the rise of epigenetics and the possible neglect of transposon dynamics, especially among biomedical scientists.

Yes! There are resilient generalizations (or "laws") in ecology.

ABSTRACT It is often argued that ecological communities admit of no useful generalizations or "laws" because these systems are especially prone to contingent historical events. Detractors respond that this argument assumes an overly stringent definition of laws of nature. Under a more relaxed conception, it is argued that ecological laws emerge at the level of communities and elsewhere. A brief review of this debate reveals an issue with deep philosophical roots that is unlikely to be resolved by a better understanding of generalizations in ecology. We therefore propose a strategy for transforming the conceptual question about the nature of ecological laws into a set of empirically tractable hypotheses about the relative re- silience of ecological generalizations across three dimensions: taxonomy, habitat type, and scale. These hypotheses are tested using a survey of 240 meta-analyses in ecology. Our central finding is that generalizations in community ecology are just as prevalent and as resilient as those in population or ecosystem ecology. These findings should help to establish community ecology as a generality-seeking science as opposed to a science of case studies. It also supports the capacity for ecologists, working at any of the three levels, to inform matters of public policy.

Distinguishing between "function" and "effect" in genome biology.

Much confusion in genome biology results from conflation of possible meanings of the word "function." We suggest that, in this connection, attention should be paid to evolutionary biologists and philosophers who have previously dealt with this problem. We need only decide that although all genomic structures have effects, only some of them should be said to have functions. Although it will very often be difficult or impossible to establish function (strictly defined), it should not automatically be assumed. We enjoin genomicists in particular to pay greater attention to parsing biological effects.

Distinguishing ecological from evolutionary approaches to transposable elements.

Considerable variation exists not only in the kinds of transposable elements (TEs) occurring within the genomes of different species, but also in their abundance and distribution. Noting a similarity to the assortment of organisms among ecosystems, some researchers have called for an ecological approach to the study of transposon dynamics. However, there are several ways to adopt such an approach, and it is sometimes unclear what an ecological perspective will add to the existing co-evolutionary framework for explaining transposon-host interactions. This review aims to clarify the conceptual foundations of transposon ecology in order to evaluate its explanatory prospects. We begin by identifying three unanswered questions regarding the abundance and distribution of TEs that potentially call for an ecological explanation. We then offer an operational distinction between evolutionary and ecological approaches to these questions. By determining the amount of variance in transposon abundance and distribution that is explained by ecological and evolutionary factors, respectively, it is possible empirically to assess the prospects for each of these explanatory frameworks. To illustrate how this methodology applies to a concrete example, we analyzed whole-genome data for one set of distantly related mammals and another more closely related group of arthropods. Our expectation was that ecological factors are most informative for explaining differences among individual TE lineages, rather than TE families, and for explaining their distribution among closely related as opposed to distantly related host genomes. We found that, in these data sets, ecological factors do in fact explain most of the variation in TE abundance and distribution among TE lineages across less distantly related host organisms. Evolutionary factors were not significant at these levels. However, the explanatory roles of evolution and ecology become inverted at the level of TE families or among more distantly related genomes. Not only does this example demonstrate the utility of our distinction between ecological and evolutionary perspectives, it further suggests an appropriate explanatory domain for the burgeoning discipline of transposon ecology. The fact that ecological processes appear to be impacting TE lineages over relatively short time scales further raises the possibility that transposons might serve as useful model systems for testing more general hypotheses in ecology.

Exploring the folkbiological conception of human nature.

Integrating the study of human diversity into the human evolutionary sciences requires substantial revision of traditional conceptions of a shared human nature. This process may be made more difficult by entrenched, 'folkbiological' modes of thought. Earlier work by the authors suggests that biologically naive subjects hold an implicit theory according to which some traits are expressions of an animal's inner nature while others are imposed by its environment. In this paper, we report further studies that extend and refine our account of this aspect of folkbiology. We examine biologically naive subjects' judgments about whether traits of an animal are 'innate', 'in its DNA' or 'part of its nature'. Subjects do not understand these three descriptions to be equivalent. Both innate and in its DNA have the connotation that the trait is species-typical. This poses an obstacle to the assimilation of the biology of polymorphic and plastic traits by biologically naive audiences. Researchers themselves may not be immune to the continuing pull of folkbiological modes of thought.