Major Life-history Transition Research Articles

Beclin-mediated Autophagy Drives Dorsal Longitudinal Flight Muscle Histolysis in the Variable Field Cricket, Gryllus lineaticeps.

Flight muscle histolysis is a widespread strategy used by insects to break down functional flight muscle and modulate the energetic costs associated with flight muscle use and maintenance. The variable field cricket, Gryllus lineaticeps, undergoes histolysis during their transition between dispersal flight and reproduction. Despite the importance of histolysis on insect reproduction and fitness, the molecular mechanisms driving this flight muscle breakdown are not well understood. Here, we show that beclin-mediated autophagy, a conserved lysosomal-dependent degradation process, drives breakdown of dorsal longitudinal flight muscle in female flight capable G. lineaticeps. We found that female G. lineaticeps activate autophagy in their dorsal longitudinal flight muscle (DLM), but to a greater extent than the neighboring dorsoventral flight muscle (DVM) during histolysis. RNA interference knockdown of beclin, a gene which encodes a critical autophagy initiation protein, delayed DLM histolysis, but did not affect DVM histolysis. This suggests that crickets selectively activate autophagy to break down the DLMs, while maintaining DVM function for other fitness-relevant activities such as walking. Overall, we confirmed that autophagy is a critical pathway used to remodel flight muscle cells during flight muscle histolysis, providing novel insights into the mechanisms underlying a major life history transition between dispersal and reproduction.

Motherhood and DREADD manipulation of the nucleus accumbens weaken established pair bonds in female prairie voles

Monogamous pair bonding has evolved to enhance reproductive success and ensure offspring survival. Although the behavioral and neural mechanisms regulating the formation of pair bonds have been relatively well outlined, how these relationships are regulated and maintained across the lifetime of an individual remains relatively unexplored. One way to explore this is to study the maintenance of a social bond across a major life-history transition. The transition to motherhood is among the most poignant moments in the life history of a female, and is associated with significant neural and behavioral changes and shifting priorities. The nucleus accumbens (NAc) is known to modulate social valence and is central to mammalian pair bonding. In this study, we investigated two mechanisms driving variation in bond strength in the socially monogamous prairie vole (Microtus ochrogaster). We manipulated neural activity of the NAc at two distinct stages of life-history, before and after the birth of offspring, to assess how neural activity and social contexts modulate female pair bond strength. Our results showed DREADD (Designer Receptor Exclusively Activated by Designer Drugs) inhibition of the NAc decreases affiliative behavior towards the mating partner, whereas DREADD activation of the NAc increases affiliative behavior of strangers, thereby decreasing social selectivity. We also found a robust “birth effect” on pair bond strength, such that bonds with partners were weakened after the birth of offspring, an effect not attributable to the amount of cohabitation time with a partner. Overall, our data support the hypotheses that NAc activity modulates reward/saliency within the social brain in different ways, and that motherhood comes with a cost for the bond strength between mating partners.

Does dispersal make the heart grow bolder? Avoidance of anthropogenic habitat elements across wolf life history

Dispersal is a fundamental ecological process that, on an individual level, is associated with intrinsic and fixed personality traits such as ‘boldness’. However, it is unknown whether personality traits or behavioural syndromes might change as a consequence of dispersal itself. We analysed 14 GPS-collared grey wolves, Canis lupus, in Finland that dispersed from their natal territories and settled in new territories, as well as 22 time-matched nondispersing controls. We used wolf avoidance of low-use forest roads, high-use primary roads and houses as proxies for boldness, and we estimated wolf responses to these features across spatial scales and across dispersal phases. Wolves, which already occupy portions of Finland with low human density, expanded into more human-impacted areas, but with a strong large-scale selection for relatively low human presence. At the finer scale, avoidance of human elements varied as a function of dispersal phase. During dispersal, avoidance of forest roads, primary roads and houses was substantially lower than in natal territories, reflecting the need to take more risks while moving in a small group (alone or with a single mate) in unfamiliar environments. After settling in new territories, the strength of avoidance of those elements continued to be lower than in natal territories, even after controlling for changes in availability. These results suggest that experiences gained across a major life-history transition, such as dispersal, might themselves influence personality traits.

Seed traits are pleiotropically regulated by the flowering time gene PERPETUAL FLOWERING 1 (PEP1) in the perennial Arabis alpina.

The life cycles of plants are characterized by two major life history transitions—germination and the initiation of flowering—the timing of which are important determinants of fitness. Unlike annuals, which make the transition from the vegetative to reproductive phase only once, perennials iterate reproduction in successive years. The floral repressor PERPETUAL FLOWERING 1 (PEP1), an ortholog of FLOWERING LOCUS C, in the alpine perennial Arabis alpina ensures the continuation of vegetative growth after flowering and thereby restricts the duration of the flowering episode. We performed greenhouse and garden experiments to compare flowering phenology, fecundity and seed traits between A. alpina accessions that have a functional PEP1 allele and flower seasonally and pep1 mutants and accessions that carry lesions in PEP1 and flower perpetually. In the garden, perpetual genotypes flower asynchronously and show higher winter mortality than seasonal ones. PEP1 also pleiotropically regulates seed dormancy and longevity in a way that is functionally divergent from FLC. Seeds from perpetual genotypes have shallow dormancy and reduced longevity regardless of whether they after‐ripened in plants grown in the greenhouse or in the experimental garden. These results suggest that perpetual genotypes have higher mortality during winter but compensate by showing higher seedling establishment. Differences in seed traits between seasonal and perpetual genotypes are also coupled with differences in hormone sensitivity and expression of genes involved in hormonal pathways. Our study highlights the existence of pleiotropic regulation of seed traits by hub developmental regulators such as PEP1, suggesting that seed and flowering traits in perennial plants might be optimized in a coordinated fashion.

Exposure to agricultural pesticide impairs visual lateralization in a larval coral reef fish

Lateralization, i.e. the preferential use of one side of the body, may convey fitness benefits for organisms within rapidly-changing environments, by optimizing separate and parallel processing of different information between the two brain hemispheres. In coral reef-fishes, the movement of larvae from planktonic to reef environments (recruitment) represents a major life-history transition. This transition requires larvae to rapidly identify and respond to sensory cues to select a suitable habitat that facilitates survival and growth. This ‘recruitment’ is critical for population persistence and resilience. In aquarium experiments, larval Acanthurus triostegus preferentially used their right-eye to investigate a variety of visual stimuli. Despite this, when held in in situ cages with predators, those larvae that previously favored their left-eye exhibited higher survival. These results support the “brain’s right-hemisphere” theory, which predicts that the right-eye (i.e. left-hemisphere) is used to categorize stimuli while the left-eye (i.e. right-hemisphere) is used to inspect novel items and initiate rapid behavioral-responses. While these experiments confirm that being highly lateralized is ecologically advantageous, exposure to chlorpyrifos, a pesticide often inadvertently added to coral-reef waters, impaired visual-lateralization. This suggests that chemical pollutants could impair the brain function of larval fishes during a critical life-history transition, potentially impacting recruitment success.

Predator effects on reef fish settlement depend on predator origin and recruit density.

During major life-history transitions, animals often experience high mortality rates due to predation, making predator avoidance particularly advantageous during these times. There is mixed evidence from a limited number of studies, however, regarding how predator presence influences settlement of coral-reef fishes and it is unknown how other potentially mediating factors, including predator origin (native vs. nonnative) or interactions among conspecific recruits, mediate the non-consumptive effects of predators on reef fish settlement. During a field experiment in the Caribbean, approximately 52% fewer mahogany snapper (Lutjanus mahogoni) recruited to reefs with a native predator (graysby grouper, Cephalopholis cruentata) than to predator-free control reefs and reefs with an invasive predator (red lionfish, Pterois volitans) regardless of predator diet. These results suggest that snapper recruits do not recognize nonnative lionfish as a threat. However, these effects depended on the density of conspecific recruits, with evidence that competition may limit the response of snapper to even native predators at the highest recruit densities. In contrast, there was no effect of predator presence or conspecific density on the recruitment of bicolor damselfish (Stegastes partitus). These context-dependent responses of coral-reef fishes to predators during settlement may influence individual survival and shape subsequent population and community dynamics.

The making of winners (and losers): how early dominance interactions determine adult social structure in a clonal fish.

Across a wide range of animal taxa, winners of previous fights are more likely to keep winning future contests, just as losers are more likely to keep losing. At present, such winner and loser effects are considered to be fairly transient. However, repeated experiences with winning and/or losing might increase the persistence of these effects, generating long-lasting consequences for social structure. To test this, we exposed genetically identical individuals of a clonal fish, the Amazon molly (Poecilia formosa), to repeated winning and/or losing dominance interactions during the first two months of their life. We subsequently investigated whether these experiences affected the fish's ability to achieve dominance in a hierarchy five months later after sexual maturity, a major life-history transition. Individuals that had only winning interactions early in life consistently ranked at the top of the hierarchy. Interestingly, individuals with only losing experience tended to achieve the middle dominance rank, whereas individuals with both winning and losing experiences generally ended up at the bottom of the hierarchy. In addition to demonstrating that early social interactions can have dramatic and long-lasting consequences for adult social behaviour and social structure, our work also shows that higher cumulative winning experience early in life can counterintuitively give rise to lower social rank later in life.

Human evolution, life history theory, and the end of biological reproduction.

Throughout primate history there have been three major life history transitions towards increasingly delayed sexual maturation and biological reproduction, as well as towards extended life expectancy. Monkeys reproduce later and live longer than do prosimians, apes reproduce later and live longer than do monkeys, and humans reproduce later and live longer than do apes. These life history transitions are connected to increased encephalization. During the last life history transition from apes to humans, increased encephalization co-evolved with increased dependence on cultural knowledge for energy acquisition. This led to a dramatic pressure for more energy investment in growth over current biological reproduction. Since the industrial revolution socioeconomic development has led to even more energy being devoted to growth over current biological reproduction. I propose that this is the beginning of an ongoing fourth major primate life history transition towards completely delayed biological reproduction and an extension of the evolved human life expectancy. I argue that the only fundamental difference between this primate life history transition and previous life history transitions is that this transition is being driven solely by cultural evolution, which may suggest some deeper evolutionary transition away from biological evolution is already in the process of occurring.

Variation in Arabidopsis flowering time associated with cis-regulatory variation in CONSTANS.

The onset of flowering, the change from vegetative to reproductive development, is a major life history transition in flowering plants. Recent work suggests that mutations in cis-regulatory mutations should play critical roles in the evolution of this (as well as other) important adaptive traits, but thus far there has been little evidence that directly links regulatory mutations to evolutionary change at the species level. While several genes have previously been shown to affect natural variation in flowering time in Arabidopsis thaliana, most either show protein-coding changes and/or are found at low frequency (<5%). Here we identify and characterize natural variation in the cis-regulatory sequence in the transcription factor CONSTANS that underlies flowering time diversity in Arabidopsis. Mutation in this regulatory motif evolved recently and has spread to high frequency in Arabidopsis natural accessions, suggesting a role for these cis-regulatory changes in adaptive variation of flowering time.

EVOLUTION OF PAEDOMORPHOSIS IN PLETHODONTID SALAMANDERS: ECOLOGICAL CORRELATES AND RE-EVOLUTION OF METAMORPHOSIS

Life-history modes can profoundly impact the biology of a species, and a classic example is the dichotomy between metamorphic (biphasic) and paedomorphic (permanently aquatic) life-history strategies in salamanders. However, despite centuries of research on this system, several basic questions about the evolution of paedomorphosis in salamanders have not been addressed. Here, we use a nearly comprehensive, time-calibrated phylogeny of spelerpine plethodontids to reconstruct the evolution of paedomorphosis and to test if paedomorphosis is (1) reversible; (2) associated with living in caves; (3) associated with relatively dry climatic conditions on the surface; and (4) correlated with limited range size and geographic dispersal. We find that paedomorphosis arose multiple times in spelerpines. We also find evidence for re-evolution of metamorphosis after several million years of paedomorphosis in a lineage of Eurycea from the Edwards Plateau region of Texas. We also show for the first time using phylogenetic comparative methods that paedomorphosis is highly correlated with cave-dwelling, arid surface environments, and small geographic range sizes, providing insights into both the causes and consequences of this major life history transition.

Phenotypic plasticity and adaptive evolution contribute to advancing flowering phenology in response to climate change

Anthropogenic climate change has already altered the timing of major life-history transitions, such as the initiation of reproduction. Both phenotypic plasticity and adaptive evolution can underlie rapid phenological shifts in response to climate change, but their relative contributions are poorly understood. Here, we combine a continuous 38 year field survey with quantitative genetic field experiments to assess adaptation in the context of climate change. We focused on Boechera stricta (Brassicaeae), a mustard native to the US Rocky Mountains. Flowering phenology advanced significantly from 1973 to 2011, and was strongly associated with warmer temperatures and earlier snowmelt dates. Strong directional selection favoured earlier flowering in contemporary environments (2010-2011). Climate change could drive this directional selection, and promote even earlier flowering as temperatures continue to increase. Our quantitative genetic analyses predict a response to selection of 0.2 to 0.5 days acceleration in flowering per generation, which could account for more than 20 per cent of the phenological change observed in the long-term dataset. However, the strength of directional selection and the predicted evolutionary response are likely much greater now than even 30 years ago because of rapidly changing climatic conditions. We predict that adaptation will likely be necessary for long-term in situ persistence in the context of climate change.

Correction: A Widespread Chromosomal Inversion Polymorphism Contributes to a Major Life-History Transition, Local Adaptation, and Reproductive Isolation

Correction: A Widespread Chromosomal Inversion Polymorphism Contributes to a Major Life-History Transition, Local Adaptation, and Reproductive Isolation

Plasticity in the timing of a major life-history transition and resulting changes in the age structure of populations of the salamander Hynobius retardatus

Variation in age and size at life-history transitions is a reflection of the diversifying influence of biotic or abiotic environmental change. Examples abound, but it is not well understood how such environmental changes influence the age structure of a population. I experimentally investigated the effects of water temperature and food type on age and body size at metamorphosis in larvae of the salamander Hynobius retardatus. In individuals grown at a cold temperature (15 °C) or given Chironomidae as prey, the time to metamorphosis was significantly prolonged, and body size at metamorphosis was significantly enlarged, compared with individuals grown at a warmer temperature (20 °C) or fed larvae. I also examined whether larval density (a possible indicator of cannibalism in natural habitats) generated variation in the age structure of natural populations in Hokkaido, Japan, where the climate is subarctic. Natural ponds in Hokkaido may contain larvae that have overwintered for 1 or 2 years, as well as larvae of the current year, and I found that the number of age classes was related to larval density. Although cool water temperatures prolong the larval period and induce later metamorphosis, in natural ponds diet-based enhancement of development translated into a shorter larval duration and earlier metamorphosis. Geographic variation in the frequency of cannibalism resulted in population differences in metamorphic timing in H. retardatus larvae. It is important to understand how environmental effects are ultimately transduced through individual organisms into population-level phenomena, with the population response arising as the summation of individual responses. Without a thorough comprehension of the mechanisms through which population and individual responses to environmental conditions are mediated, we cannot interpret the relationship between population-level and individual-level phenomena. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102, 100–114.

A widespread chromosomal inversion polymorphism contributes to a major life-history transition, local adaptation, and reproductive isolation.

Author SummaryGenome rearrangements that change the order of genes along a chromosome are known as inversions and have long been hypothesized to be involved in the origin of species. Yet the way inversions contribute to adaptation and speciation remains mysterious. In this study, we identified a geographically widespread adaptive inversion polymorphism in the yellow monkeyflower, Mimulus guttatus. One arrangement of the inverted region is found in an annual ecotype of this species that lives in Mediterranean habitats characterized by reduced soil water availability in the summer. The other arrangement appears in a perennial ecotype that lives in habitats with high year-round soil moisture. The inversion was observed to influence morphological and flowering time differences between these ecotypes across most of western North America. To test whether the inversion polymorphism contributes to adaptation and reproductive isolation, we conducted a field experiment by breeding plants to reciprocally swap the alternative chromosomal arrangements between the annual and perennial genetic backgrounds. We demonstrated that this inversion polymorphism contributes to local adaptation, the annual/perennial life-history transition, and three reproductive isolating barriers. These results are consistent with the theory that adaptation to local environments can drive the spread of chromosomal inversions and promote speciation.

Multiple gains and losses of Wolbachia symbionts across a tribe of fungus‐growing ants

Although the intracellular bacterium Wolbachia is ubiquitous in insects, it has a unique relationship with New World ants on which particular bacterial strains have specialized. However, data are from distantly related hosts and detailed phylogenetic information which could reveal transmission dynamics are lacking. Here, we investigate host-Wolbachia relationships in the monophyletic fungus-growing ant tribe Attini, screening 23 species and using multilocus sequence typing to reliably identify Wolbachia strains. This technique reduces the significant problem of recombination seen using traditional single gene techniques. The relationship between Wolbachia and the fungus-growing ants appears complex and dynamic. There is evidence of co-cladogenesis, supporting vertical transmission; however, this is incomplete, demonstrating that horizontal transmission has also occurred. Importantly, the infection prevalence is frequently different between closely related taxa, with the Acromyrmex leaf-cutting ants appearing particularly prone to infection and there being no consistent relationship with any of the major life history transitions. We suggest that infection loss and horizontal transmission have driven epidemics or selective sweeps of Wolbachia, resulting in multiple gains and losses of infection across the fungus-growing ants.

Major life-history transitions by deterministic directional natural selection

For large-scale evolution on Earth there has been a directional change where simple self-replicators evolved into large organisms with high metabolic rates and long pre-reproductive periods. Associated with this increase there have been major life-history transitions from asomatic, non-senescing, haploid, and asexually reproducing organisms to somatic, senescing, diploid, and sexually reproducing organisms with male and female individuals. Using a game theoretical model, it is shown that this trajectory can be explained by deterministic natural selection as it arises from first principles of the self-replication process in mobile organisms. It is shown (i) that selection for an increase in the energetic state of the organism puts a direction to evolution, (ii) that selection by density-dependent competitive interactions can explain the major life-history transitions as a function of the energetic state of the organism, and (iii) that the two selection processes combined can explain an exponentially increasing body mass. It is also shown (iv) why, for the case with an increasing body mass, we may expect many life histories to evolve in accordance with the exponents of the body mass allometries, (v) that an upper constraint on the body mass and metabolic rate can induce an additional transition into eusocial communities, and (vi) that the evolutionary trajectory is likely reversible with backward evolution during periods of environmental crises.

SELECTIVE MORTALITY DURING THE LARVAL–JUVENILE TRANSITION IN TWO CORAL REEF FISHES

For organisms with complex life histories, processes occurring during transitions between stages can strongly affect population dynamics. The major life history transition for many marine species is settlement from pelagic larvae to benthic or demersal juveniles. We examined differential mortality at settlement as a function of early life history traits (size-at-age, growth rates) in three cohorts of two common Caribbean coral reef fishes, Thalassoma bifasciatum and Halichoeres bivittatus (Labridae). We deployed light traps to collect late-stage larvae of each cohort. We also collected juveniles of each cohort at regular intervals (every second day) for two weeks following their first appearance on the nearshore reefs of Barbados, West Indies, during the spring (April–May) and fall (August–October) of 1997. Comparisons of otolith-derived traits exhibited by younger recruits (initial group) to those exhibited by older juveniles (survivor group) revealed that there was a difference in otolith growth during ...

Incongruence Between Morphological Data Sets: An Example from the Evolution of Endoparasitism Among Parasitic Wasps (Hymenoptera: Braconidae)

Phylogenetic analyses of molecular and morphological data sets for a group of parasitic wasps(Hymenoptera: Braconidae)givestrikinglydifferentresults.Themoleculardata indicatethat the major life history transition from ectoparasitism to endoparasitism has occurred independently several times within thefamily whilethemorphological data indicatea singleorigin. Similar incon- gruent topologies are obtained if the morphological data are partitioned by either of two methods: distinguishing (1) characters of the larval stage and female reproductive system, or (2) characters selected individually by the authors prior to the analysis as likely to be mechanistically associated with endo/ectoparasitism. This result is supported by signiecant differences in tests of incongru- ence, and we propose that it is caused by convergence among morphological characters resulting fromashared lifehistory strategy.(Coneict;convergence;homoplasy;Hymenoptera;incongruence; parasitoid.)

A General Theory of Evolution: By Means of Selection by Density Dependent Competitive Interactions.Lars Witting

Previous articleNext article No AccessNew Biological BooksA General Theory of Evolution: By Means of Selection by Density Dependent Competitive Interactions. Lars Witting John C. KricherJohn C. Kricher Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The Quarterly Review of Biology Volume 73, Number 4Dec., 1998 Published in association with Stony Brook University Article DOIhttps://doi.org/10.1086/420451 Views: 3Total views on this site Citations: 2Citations are reported from Crossref Copyright 1998 The University of ChicagoPDF download Crossref reports the following articles citing this article:Lars Witting Major life-history transitions by deterministic directional natural selection, Journal of Theoretical Biology 225, no.33 (Dec 2003): 389–406.https://doi.org/10.1016/S0022-5193(03)00274-1Lars Witting From Asexual to Eusocial Reproduction by Multilevel Selection by Density-Dependent Competitive Interactions, Theoretical Population Biology 61, no.22 (Mar 2002): 171–195.https://doi.org/10.1006/tpbi.2001.1561

Phylogenetic Relationships between Oviparous and Viviparous Populations of an Australian Lizard (Lerista bougainvillii,Scincidae)

Viviparity has evolved from oviparity in many vertebrate lineages, and species that contain both oviparous and viviparous populations offer the best opportunity for a detailed examination of the processes involved in this major life-history transition. However, although several such species have been reported, none have been the subject of detailed phylogenetic analyses. We examine such a case within the Australian scincid lizardLerista bougainvillii.Data were obtained by sequencing a 314-bp segment of mitochondrial cytochromebfrom 32 individuals from 17 populations ofL. bougainvilliiand two morphologically similar congeneric species (L. dorsalisandL. microtus). Sequences were aligned and analyzed using parsimony and distance methods. The resultant matriarchal phylogeny resolved the populations ofL. bougainvilliiinto three major groups: a population from NSW; a group predominantly from Eyre Peninsula; and a less well-defined group from the central part of the species range. The NSW and Eyre Peninsula groups are oviparous and are quite divergent from otherL. bougainvilliipopulations and from each other. The central group contains both viviparous and oviparous populations, and seems to represent a more recent radiation within the species. Our results indicate that viviparity has evolved at least twice within the genusLerista,because the viviparousL. microtusis not closely related to viviparous populations ofL. bougainvillii.The lack of phylogenetic separation of mtDNAs from viviparous and oviparous populations withinL. bougainvilliirelative to strong geographic structure within the latter indicates that populations with different reproductive modes are indeed conspecific.Lerista bougainvilliiis thus the first vertebrate species for which intraspecific bimodality in reproductive mode can be claimed with any certainty.