Joan Roughgarden | |
---|---|
Born | Paterson, New Jersey, U.S. | 13 March 1946
Alma mater | University of Rochester |
Known for | Critiques of sexual selection, theory of social selection |
Scientific career | |
Fields | Ecology and evolutionary biology |
Institutions | University of Massachusetts Boston Stanford University Hawaiʻi Institute of Marine Biology |
Thesis | Implications of density dependent natural selection (1971) |
Joan Roughgarden (born 13 March 1946) is an American ecologist and evolutionary biologist. She has engaged in theory and observation of coevolution and competition in Anolis lizards of the Caribbean, and recruitment limitation in the rocky intertidal zones of California and Oregon. She has more recently become known for her rejection of sexual selection, her theistic evolutionism, and her work on holobiont evolution.
Roughgarden was born in Paterson, New Jersey, United States. She received a Bachelor of Science in biology (with Distinction and Phi Beta Kappa) and a Bachelor of Arts in Philosophy with highest honors from University of Rochester in 1968 and later a Ph.D. in biology from Harvard University in 1971. In 1998, Roughgarden came out as transgender and changed her name to Joan, making a coming out post on her website on her 52nd birthday. [1]
Roughgarden worked as an instructor and Assistant Professor of Biology at the University of Massachusetts Boston from 1970 to 1972. In 1972 she joined the faculty of the Department of Biology at Stanford University. After becoming full professor she retired in 2011, and became Emeritus Professor. She founded and directed the Earth Systems Program at Stanford and has received awards for service to undergraduate education. In 2012 she moved to Hawaii, where she became an adjunct professor at the Hawaiʻi Institute of Marine Biology. In her academic career, Roughgarden advised 20 Ph.D. students and 15 postdoctoral fellows. [2]
Roughgarden has authored books and over 180 scientific articles. In addition to a textbook on ecological and evolutionary theory in 1979, Roughgarden has carried out ecological field studies with Caribbean lizards and with barnacles and their larvae along the California coast. In 2015, she wrote the fiction novel Ram-2050, a science-fiction retelling of the Ramayana.
Roughgarden's early work in the 1970s and 80s helped to develop the Anolis lizards of the Caribbean as an important model system for evolution and ecology. For example, she used two-species enclosure experiments on two Caribbean islands to demonstrate increasing strength of interspecific competition as resource partitioning decreases: [3] a central tenet for competition theory. The Anolis system thus provided an early example of an eco-evolutionary feedback, [4] and with further development by Jonathan Losos and others, has become an important example of adaptive radiation.
After setting up a lab at the Hopkins Marine Station, Roughgarden sought to extend her approach of combining theoretical with field research by studying intertidal acorn barnacles ( Balanus and Chthamalus spp). Earlier work by Joseph Connell, Bob Paine and others had suggested that the characteristic zonation of rocky intertidal communities was predominantly structured by predation, [5] (for example by Pisaster seastars) and by competition, [6] [7] wherein dominant Balanus species displaced Chthamalus species to the high intertidal zones. Together with her student, Steve Gaines, Roughgarden showed that these interspecific interactions were most important in intertidal localities and communities with a high density of barnacles, such as those Connell and others had studied in Scotland. [6] [8] At Hopkins in Central California, however, barnacle density was lower, and the amount of free space was best explained by periodic pulses of larval recruitment. [8] With her student Sean Connolly, she then showed, through both empirical observation and modeling, that a latitudinal gradient in upwelling along the west coast of North America created very dense barnacle recruitment in the north (Oregon and Washington), where upwelling was weak, and very sparse barnacle recruitment in the south (California), where upwelling was strong. [9] This in turn explained why field studies in the north had found interspecific interactions to be important, while her own field studies in the south had found larval recruitment to be most important for structuring intertidal populations. [10] This deft synthesis helped to drive a paradigm shift in marine ecology which emphasized larval dispersal and recruitment dynamics over adult interactions and favored demographic models of populations open to larval recruits from distant localities, which dominated the field during the 1990s. [11]
Around the time of her transition, Roughgarden began to shift her research focus to Darwin's theory of sexual selection. In her 2004 book, Evolution's Rainbow, [12] Roughgarden analyzes how biology can influence human sexuality and gender identity and explores the substantial diversity of mating systems and sexuality throughout the animal kingdom, with an eye toward understanding human sexual categories like gay, lesbian, and trans. In this book, and other articles around the same time, she offered criticism of sexual selection theory [13] [14] [15] by providing examples of species that depart from its predictions (such as homosexual behavior in bonobos, elephants and lizards) as well as highlighting contradictions between population genetic theory and sexual selection theory. She also provided the beginnings of an alternative theory to sexual selection called social selection, which she describes as being focused on natural selection based on differential offspring production, where sexual selection is focused on differential mating success.
A 2006 article in the journal Science with her student Erol Akçay, and Meeko Oishi, formally presented the theory of social selection in terms of game theory. [16] Beyond the Nash Competitive Equilibrium (NCE) imported to evolutionary biology by John Maynard Smith as the Evolutionary Stable Strategy, Roughgarden et al. discuss the Nash Bargaining Solution (NBS), which exists as an alternative to the NCE that is reached through negotiation. When playing in developmental time (as opposed to evolutionary time), a game player that stands to lose individual fitness at an NCE relative to its competitor may establish a threat point by promising to play a sub-optimal strategy. Through negotiation, for example via a side payment, the players can arrive at an NBS through playing mixed strategies across repeated games which thereby maximizes the fitness of the cooperative "team" (which consists of both players) rather than to any one player. Roughgarden et al. provide several examples of what such cooperative game play would look like in nature, and then define the evolutionary theory of social selection as one which considers such cooperative team games in the developmental tier as the primitive state, with sexual conflict as the derived state. They argue that social selection theory is mutually exclusive with the evolutionary theory of sexual selection, which treats sexual conflict as the primitive state and sexual cooperation as derived.
Following the Science paper, forty scientists produced ten critical letters [17] [18] stating that the article was misleading, that it contained misunderstandings and misrepresentations, that sexual selection accounted for all the data presented and subsumed Roughgarden's theoretical analysis, and that sexual selection explained data that her theory could not. [17] [18] Troy Day stated that "many people felt that this was completely shoddy science and poor scholarship, all motivated by a personal agenda". [17] Roughgarden stated she was "not altogether surprised" by the volume of dissent and that her theory was not an extension of sexual selection theory. [17] [18]
Tim Clutton-Brock of Oxford University wrote a more detailed rebuttal in Science in 2007, [19] in which he concedes the point that males can engage in sexual selection on females, even in species where the operational sex ratio is biased towards males, stating: "Consequently, satisfactory explanations of the evolution of sex differences requires an understanding of the operation of sexual selection in females as well as males". [19] Nevertheless, Clutton-Brock concludes that sexual selection is a robust theoretical framework, without ever addressing the theoretical distinction in the polarity of intersexual cooperation and conflict highlighted by Roughgarden et al. [16]
In her 2009 book The Genial Gene, [20] Roughgarden continues to build a case against sexual selection theory and to present social selection theory as an alternative. The book is titled as a response to the popular book, The Selfish Gene, by Richard Dawkins, [21] which expounds what Roughgarden describes a "neo-Spencerian" view of nature "red in tooth and claw" in which competition and conflict dominate. In The Genial Gene, after an initial section defining and attacking sexual selection, followed by a definition of social selection as one based on differences in offspring-production, rather than differences in mating success.
A second section is focused on the genetic basis of social selection. The first chapter addresses how sexual reproduction evolved in the first place, and makes the case for Roughgarden's Portfolio hypothesis, which emphasizes that sexual reproduction creates genetic diversity through recombination, as opposed to the more commonly favored Muller's ratchet, which emphasizes that sex removes deleterious mutations through recombination. The second chapter explains the binary distribution of gamete types (sperm vs. egg) as a strategy to maximize gametic contact, rather than as a result of conflicting gametic strategies. A final chapter argues that hermaphroditism, rather than gonochorism, is the primitive state of sexuality.
The third section takes a two-tier approach to developing social selection theory. A behavioral tier focuses on game theory and Nash Bargaining Solutions as outlined in her 2006 paper. [16] A second population genetic tier is then described that operates as a result of many replays of the behavioral tier. The book concludes by listing 26 phenomena that, according to Roughgarden, are explained differently by sexual selection theory and are better explained by social selection theory. She says that sexual selection theory derives from a view of natural behavior predicated on the selfish-gene concept, competition and deception, whereas the social-selection theory derives from teamwork, honesty, and genetic equality. As of 2012 she has continued to study if social selection as opposed to sexual selection is a more important driver of evolution for colonial species such as corals or perhaps humans. [22] [23]
Roughgarden's criticism of sexual selection has been rejected by the scientific community, and her papers on it have received few citations in scientific literature. [24] In a 2019 interview, she stated that "Most biologists remain defensive of sexual selection theory". [15]
In 2013, Roughgarden funded a Catalysis meeting at the National Evolutionary Synthesis Center with the goal of debating and reviewing "the status of sexual selection studies and to indicate challenges and future directions". [25] The group struggled to come to a consensus definition of sexual selection, but a subgroup offered a definition that for the first time explicitly differentiated fecundity selection for sexual selection sensu stricto. [25]
Roughgarden has written on the relationship between Christianity and science. [26] Her book Evolution and Christian Faith: Reflections of an Evolutionary Biologist presents scripture passages that emphasize her belief that the Bible does not conflict with evolutionary biology and relates Christianity and evolution by asserting that all life is interconnected, as members of a faith community are connected. Roughgarden opposes creationism and intelligent design, but asserts her belief in God's involvement in evolution. [27] She was a speaker at the Beyond Belief symposium in 2006. [28]
As professor emerita, Dr. Roughgarden turned her attention to the emerging concept of the holobiont, which she defined as "an animal or plant host together with all the microbes living on or in it, exosymbionts and endosymbionts, respectively. [29] " The concept, which originated in 1943, has had increasing recognition with the rise of second and third-generation DNA sequencing methods that allow the microbial communities (i.e. the microbiome) of a host to be examined. The close association between the microbiome and its host has led many [30] [31] [32] to suggest that the holobiont may be an evolutionary unit of selection, in which the combination of the host's genes with those of its microbiome produce an extended genome, or hologenome. However, the hologenome concept has been criticized on the grounds that microbiomes are usually not vertically transmitted from parent to child, [33] thereby violating what is commonly thought to be one of the key principles of natural selection: variation inherited in a Mendelian fashion.
Together with other proponents of the holobiont concept, Roughgarden wrote a 2018 review of the topic [29] in which they examined the evidence for the holobiont as a biological entity. They considered the tight integration of physiological, developmental, reproductive and even immunological components between host and microbial symbionts to provide a foundation for this concept. For example mammalian mothers' milk contains sugars that appear to be for the benefit of the microbial symbionts, because they cannot be metabolized by the newborn. [34] They also cite the horizontal acquisition of DNA coding for syncytin, [35] a protein that allows formation of the placenta, as a key step in the evolution of placental mammals, which also demonstrates adaptive evolution in the holobiont.
In this review, [29] Roughgarden begins to sketch a population genetic model of holobiont evolution, containing a host species, and a single microbial symbiont, and in which selection is based only on the number of copies of the symbiont genome acquired by the host. The model contains three sequential processes per generation: microbes can move between hosts, they can proliferate within hosts and holobionts can survive or perish dependent on the number of symbionts acquired. This model was enough to show that, with vertical transmission, a deleterious symbiont will reduce the number of holobionts (and symbionts), while a beneficial symbiont will tend to increase the sizes of both groups. However, horizontal transmission "binds the collection of microbiomes into a unified system, a meta-community, rather than a collection of independent communities".
Roughgarden followed this review with two papers [36] [37] that further fleshed out her model of holobiont evolution. The first [36] showed that, when microbes colonize hosts following a Poisson distribution, horizontal transmission can still lead to holobiont evolution when beneficial symbionts increase the success of their hosts and thus flood the microbial source pool (the converse case with parasitic microbes also holds true). She calls this phenomenon "collective inheritance" as opposed to lineal Mendelian inheritance. The second paper [37] adds a second microbial species to the model, as well as a "colonization parameter" d, which partially determines the Poisson rate parameter. The d parameter approximates the density of the symbiont strain around the host, or the host's selectivity for the symbiont species, depending on context. Because microbial colonization of the host follows a Poisson distribution, there is no Hardy-Weinberg analog, and directional selection tends to be more diffuse than expectated under vertical transmission. She then reasons from this two-microbe model that the host is likely to use antibodies and "probodies" to modulate d for each microbial species, in effect orchestrating things so that only microbes that provide some minimum amount of altruism toward their host are allowed to remain in symbiosis with the host. From the microbe's standpoint, those species that provide the minimum amount of altruism to clear the host's threshold will tend to outcompete those that provide more. This paper [37] carefully demonstrates that this host-orchestrated species selection process is conceptually distinct from co-evolution or multi-level selection and can predict and explain the tight integration of hosts and their microbial symbionts found throughout the eukaryotic tree of life.
Roughgarden has served as associate editor of several academic journals, including Philosophy and Theory in Biology (since 2008), American Naturalist (1984–1989), Oecologia (1979–1982), and Theoretical Population Biology (1975–1986). She was the vice-chair and Chair of Theoretical Ecology Section of the Ecological Society of America during 2002–2003. She has served on the Nonprofit Organization Board for the Oceanic Society (San Francisco), the EPA Science Advisory Board Committee on Valuating the Protection of Ecological Systems and Services, and the science advisory boards of the Pacific Ocean Conservation Network (California), and the Channel Islands National Marine Sanctuary (Santa Barbara). [40]
Horizontal transmission is the transmission of organisms between biotic and/or abiotic members of an ecosystem that are not in a parent-progeny relationship. Because the evolutionary fate of the agent is not tied to reproductive success of the host, horizontal transmission tends to evolve virulence. It is therefore a critical concept for evolutionary medicine.
Microbiota are the range of microorganisms that may be commensal, mutualistic, or pathogenic found in and on all multicellular organisms, including plants. Microbiota include bacteria, archaea, protists, fungi, and viruses, and have been found to be crucial for immunologic, hormonal, and metabolic homeostasis of their host.
Nancy A. Moran is an American evolutionary biologist and entomologist, University of Texas Leslie Surginer Endowed Professor, and co-founder of the Yale Microbial Diversity Institute. Since 2005, she has been a member of the United States National Academy of Sciences. Her seminal research has focused on the pea aphid, Acyrthosiphon pisum and its bacterial symbionts including Buchnera (bacterium). In 2013, she returned to the University of Texas at Austin, where she continues to conduct research on bacterial symbionts in aphids, bees, and other insect species. She has also expanded the scale of her research to bacterial evolution as a whole. She believes that a good understanding of genetic drift and random chance could prevent misunderstandings surrounding evolution. Her current research goal focuses on complexity in life-histories and symbiosis between hosts and microbes, including the microbiota of insects.
The hologenome theory of evolution recasts the individual animal or plant as a community or a "holobiont" – the host plus all of its symbiotic microbes. Consequently, the collective genomes of the holobiont form a "hologenome". Holobionts and hologenomes are structural entities that replace misnomers in the context of host-microbiota symbioses such as superorganism, organ, and metagenome. Variation in the hologenome may encode phenotypic plasticity of the holobiont and can be subject to evolutionary changes caused by selection and drift, if portions of the hologenome are transmitted between generations with reasonable fidelity. One of the important outcomes of recasting the individual as a holobiont subject to evolutionary forces is that genetic variation in the hologenome can be brought about by changes in the host genome and also by changes in the microbiome, including new acquisitions of microbes, horizontal gene transfers, and changes in microbial abundance within hosts. Although there is a rich literature on binary host–microbe symbioses, the hologenome concept distinguishes itself by including the vast symbiotic complexity inherent in many multicellular hosts.
The phycosphere is a microscale mucus region that is rich in organic matter surrounding a phytoplankton cell. This area is high in nutrients due to extracellular waste from the phytoplankton cell and it has been suggested that bacteria inhabit this area to feed on these nutrients. This high nutrient environment creates a microbiome and a diverse food web for microbes such as bacteria and protists. It has also been suggested that the bacterial assemblages within the phycosphere are species-specific and can vary depending on different environmental factors.
A microbiome is the community of microorganisms that can usually be found living together in any given habitat. It was defined more precisely in 1988 by Whipps et al. as "a characteristic microbial community occupying a reasonably well-defined habitat which has distinct physio-chemical properties. The term thus not only refers to the microorganisms involved but also encompasses their theatre of activity". In 2020, an international panel of experts published the outcome of their discussions on the definition of the microbiome. They proposed a definition of the microbiome based on a revival of the "compact, clear, and comprehensive description of the term" as originally provided by Whipps et al., but supplemented with two explanatory paragraphs, the first pronouncing the dynamic character of the microbiome, and the second clearly separating the term microbiota from the term microbiome.
Microbial symbiosis in marine animals was not discovered until 1981. In the time following, symbiotic relationships between marine invertebrates and chemoautotrophic bacteria have been found in a variety of ecosystems, ranging from shallow coastal waters to deep-sea hydrothermal vents. Symbiosis is a way for marine organisms to find creative ways to survive in a very dynamic environment. They are different in relation to how dependent the organisms are on each other or how they are associated. It is also considered a selective force behind evolution in some scientific aspects. The symbiotic relationships of organisms has the ability to change behavior, morphology and metabolic pathways. With increased recognition and research, new terminology also arises, such as holobiont, which the relationship between a host and its symbionts as one grouping. Many scientists will look at the hologenome, which is the combined genetic information of the host and its symbionts. These terms are more commonly used to describe microbial symbionts.
Eugene Rosenberg is a microbiologist at the Faculty of Life Sciences at Tel Aviv University, an expert in the field of applied environmental microbiology, in particular his work on Myxobacteria, microorganisms to combat pollution (bioremediation), and the Hologenome theory of evolution.
A holobiont is an assemblage of a host and the many other species living in or around it, which together form a discrete ecological unit through symbiosis, though there is controversy over this discreteness. The components of a holobiont are individual species or bionts, while the combined genome of all bionts is the hologenome. The holobiont concept was initially introduced by the German theoretical biologist Adolf Meyer-Abich in 1943, and then apparently independently by Dr. Lynn Margulis in her 1991 book Symbiosis as a Source of Evolutionary Innovation. The concept has evolved since the original formulations. Holobionts include the host, virome, microbiome, and any other organisms which contribute in some way to the functioning of the whole. Well-studied holobionts include reef-building corals and humans.
Social selection is a term used with varying meanings in biology.
Hologenomics is the omics study of hologenomes. A hologenome is the whole set of genomes of a holobiont, an organism together with all co-habitating microbes, other life forms, and viruses. While the term hologenome originated from the hologenome theory of evolution, which postulates that natural selection occurs on the holobiont level, hologenomics uses an integrative framework to investigate interactions between the host and its associated species. Examples include gut microbe or viral genomes linked to human or animal genomes for host-microbe interaction research. Hologenomics approaches have also been used to explain genetic diversity in the microbial communities of marine sponges.
In the field of microbiome research, a group of species is said to show a phylosymbiotic signal if the degree of similarity between the species' microbiomes recapitulates to a significant extent their evolutionary history. In other words, a phylosymbiotic signal among a group of species is evident if their microbiome similarity dendrogram could prove to have significant similarities with their host's phylogenic tree. For the analysis of the phylosymbiotic signal to be reliable, environmental differences that could shape the host microbiome should be either eliminated or accounted for. One plausible mechanistic explanation for such phenomena could be, for example, a result of host immune genes that rapidly evolve in a continuous arms race with members of its microbiome.
Vertical transmission of symbionts is the transfer of a microbial symbiont from the parent directly to the offspring. Many metazoan species carry symbiotic bacteria which play a mutualistic, commensal, or parasitic role. A symbiont is acquired by a host via horizontal, vertical, or mixed transmission.
All animals on Earth form associations with microorganisms, including protists, bacteria, archaea, fungi, and viruses. In the ocean, animal–microbial relationships were historically explored in single host–symbiont systems. However, new explorations into the diversity of marine microorganisms associating with diverse marine animal hosts is moving the field into studies that address interactions between the animal host and a more multi-member microbiome. The potential for microbiomes to influence the health, physiology, behavior, and ecology of marine animals could alter current understandings of how marine animals adapt to change, and especially the growing climate-related and anthropogenic-induced changes already impacting the ocean environment.
The plant microbiome, also known as the phytomicrobiome, plays roles in plant health and productivity and has received significant attention in recent years. The microbiome has been defined as "a characteristic microbial community occupying a reasonably well-defined habitat which has distinct physio-chemical properties. The term thus not only refers to the microorganisms involved but also encompasses their theatre of activity".
Since the colonization of land by ancestral plant lineages 450 million years ago, plants and their associated microbes have been interacting with each other, forming an assemblage of species that is often referred to as a holobiont. Selective pressure acting on holobiont components has likely shaped plant-associated microbial communities and selected for host-adapted microorganisms that impact plant fitness. However, the high microbial densities detected on plant tissues, together with the fast generation time of microbes and their more ancient origin compared to their host, suggest that microbe-microbe interactions are also important selective forces sculpting complex microbial assemblages in the phyllosphere, rhizosphere, and plant endosphere compartments.
The holobiont concept is a renewed paradigm in biology that can help to describe and understand complex systems, like the host-microbe interactions that play crucial roles in marine ecosystems. However, there is still little understanding of the mechanisms that govern these relationships, the evolutionary processes that shape them and their ecological consequences. The holobiont concept posits that a host and its associated microbiota with which it interacts, form a holobiont, and have to be studied together as a coherent biological and functional unit to understand its biology, ecology, and evolution.
Catalina Cuellar-Gempeler is a Colombian microbial ecologist and marine microbiologist, currently an Associate Professor at Cal Poly Humboldt. Her research focuses on understanding microbial metacommunity dynamics, eco-evolutionary dynamics, and ecosystem dynamics. Her research group, the CGlab uses host associated microbial communities as a model system to understand how processes of community assembly result in patterns of diversity and function. The lab's main emphasis is on the microbes used in digestion in the Californian and Eastern carnivorous pitcher plants. In March 2021, Cuellar-Gempeler was awarded an Early Career grant of $1 million by the National Science Foundation.
Megan Frederickson is a Canadian evolutionary biologist who is a professor of Ecology and Evolutionary Biology at the University of Toronto. Her research considers the evolution of cooperation and the ecological genetics of mutualism.
Sponge microbiomes are diverse communities of microorganisms in symbiotic association with marine sponges as their hosts. These microorganisms include bacteria, archaea, fungi, viruses, among others. The sponges have the ability to filter seawater and recycle nutrients while providing a safe habitat to many microorganisms, which provide the sponge host with fixed nitrogen and carbon, and stimulates the immune system. Together, a sponge and its microbiome form a holobiont, with a single sponge often containing more than 40 bacterial phyla, making sponge microbial environments a diverse and dense community. Furthermore, individual holobionts work hand in hand with other near holobionts becoming a nested ecosystem, affecting the environment at multiple scales.
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