Sex reduces genetic variation: a multidisciplinary review

For over a century, the paradigm has been that sex invariably increases genetic variation, despite many renowned biologists asserting that sex decreases most genetic variation. Sex is usually perceived as the source of additive genetic variance that drives eukaryotic evolution vis-à-vis adaptation and Fisher's fundamental theorem. However, evidence for sex decreasing genetic variation appears in ecology, paleontology, population genetics, and cancer biology. The common thread among many of these disciplines is that sex acts like a coarse filter, weeding out major changes, such as chromosomal rearrangements (that are almost always deleterious), but letting minor variation, such as changes at the nucleotide or gene level (that are often neutral), flow through the sexual sieve. Sex acts as a constraint on genomic and epigenetic variation, thereby limiting adaptive evolution. The diverse reasons for sex reducing genetic variation (especially at the genome level) and slowing down evolution may provide a sufficient benefit to offset the famed costs of sex.     

Complex evolutionary transitions and the significance of c(3)-c(4) intermediate forms of photosynthesis in Molluginaceae

C(4) photosynthesis is a series of biochemical and structural modifications to C(3) photosynthesis that has evolved numerous times in flowering plants, despite requiring modification of up to hundreds of genes. To study the origin of C(4) photosynthesis, we reconstructed and dated the phylogeny of Molluginaceae, and identified C(4) taxa in the family. Two C(4) species, and three clades with traits intermediate between C(3) and C(4) plants were observed in Molluginaceae. C(3)-C(4) intermediacy evolved at least twice, and in at least one lineage was maintained for several million years. Analyses of the genes for phosphoenolpyruvate carboxylase, a key C(4) enzyme, indicate two independent origins of fully developed C(4) photosynthesis in the past 10 million years, both within what was previously classified as a single species, Mollugo cerviana. The propensity of Molluginaceae to evolve C(3)-C(4) and C(4) photosynthesis is likely due to several traits that acted as developmental enablers. Enlarged bundle sheath cells predisposed some lineages for the evolution of C(3)-C(4) intermediacy and the C(4) biochemistry emerged via co-option of photorespiratory recycling in C(3)-C(4) intermediates. These evolutionarily stable transitional stages likely increased the evolvability of C(4) photosynthesis under selection environments brought on by climate and atmospheric change in recent geological time.     

Evolution of extreme body size disparity in monitor lizards (Varanus)

Many features of species' biology, including life history, physiology, morphology, and ecology are tightly linked to body size. Investigation into the causes of size divergence is therefore critical to understanding the factors shaping phenotypic diversity within clades. In this study, we examined size evolution in monitor lizards (Varanus), a clade that includes the largest extant lizard species, the Komodo dragon (V. komodoensis), as well as diminutive species that are nearly four orders of magnitude smaller in adult body mass. We demonstrate that the remarkable body size disparity of this clade is a consequence of different selective demands imposed by three major habitat use patterns-arboreality, terrestriality, and rock-dwelling. We reconstructed phylogenetic relationships and ancestral habitat use and applied model selection to determine that the best-fitting evolutionary models for species' adult size are those that infer oppositely directed adaptive evolution associated with terrestriality and rock-dwelling, with terrestrial lineages evolving extremely large size and rock-dwellers becoming very small. We also show that habitat use affects the evolution of several ecologically important morphological traits independently of body size divergence. These results suggest that habitat use exerts a strong, multidimensional influence on the evolution of morphological size and shape disparity in monitor lizards.     

Evolution of a plastic quantitative trait in an age-structured population in a fluctuating environment

We analyze weak fluctuating selection on a quantitative character in an age-structured population not subject to density regulation. We assume that early in the first year of life before selection, during a critical state of development, environments exert a plastic effect on the phenotype, which remains constant throughout the life of an individual. Age-specific selection on the character affects survival and fecundity, which have intermediate optima subject to temporal environmental fluctuations with directional selection in some age classes as special cases. Weighting individuals by their reproductive value, as suggested by Fisher, we show that the expected response per year in the weighted mean character has the same form as for models with no age structure. Environmental stochasticity generates stochastic fluctuations in the weighted mean character following a first-order autoregressive model with a temporally autocorrelated noise term and stationary variance depending on the amount of phenotypic plasticity. The parameters of the process are simple weighted averages of parameters used to describe age-specific survival and fecundity. The "age-specific selective weights" are related to the stable distribution of reproductive values among age classes. This allows partitioning of the change in the weighted mean character into age-specific components.     

Molecular systematics of the Amazonian endemic genus Hylexetastes (Aves: Dendrocolaptidae): taxonomic and conservation implications

Hylexetastes woodcreepers are endemic to the terra firme forests of the Amazon basin. Currently, most taxonomic sources recognize two species of Hylexetastes (H. perrotii and H. stresemanni), each divided into three subspecies. Some authors maintain that the H. perrotii subspecies should be elevated to full species status. In particular, Hylexetastes perrotii brigidai is endemic to the eastern Amazon, the second Amazonian area of endemism (Xingu) most affected by deforestation and habitat degradation. Consequently, the taxonomic status of H. p. brigidai is of particular concern for conservation. Thus far, only morphological characters have been evaluated for the taxonomic delimitation of species and subspecies of Hylexetastes. We present a molecular phylogenetic analysis of all subspecies to help delimit Hylexetastes interspecific limits. Fragments of two mitochondrial (Cytb and ND2) and three nuclear genes (FGB5, G3PDH and MUSK) from 57 Hylexetastes specimens were sequenced. An ecological niche model was estimated to describe more accurately the potential distributions of taxa and to evaluate their vulnerability to ongoing deforestation. Phylogenetic analyses support the paraphyly of the polytypic H. perrotii as currently delimited and the elevation of Hylexetastes perrotii uniformis to full species rank, as well as the presence of three evolutionary significant units (ESUs) within this newly delimited species, including one grouping all H. p. brigidai specimens. Alternatively, under lineage-based species concepts, our results support at least five evolutionary species in Hylexetastes: H. stresemanni, H. undulatus, H. perrotii, H. uniformis and H. brigidai. Each of these taxa and ESUs are distributed in different interfluvial areas of the Amazon basin, which have different degrees of disturbance. Because they occupy the most heavily impacted region among all Hylexetastes ESUs, regular assessments of the conservation statuses of H. p. brigidai and both H. uniformis ESUs are paramount.     

Ecological insights into the underlying evolutionary patterns of biofilm formation from biological wastewater treatment systems: Red or Black Queen Hypothesis?

Interspecies interactions and phylogenetic distances were studied to reveal the underlying evolutionary adaptations of biofilms sourced from wastewater treatment processes. Based on 380 pairwise cocultures of 40 strains from two microbial aggregates (surface-attached and mobile aggregates [flocs]) at two substrate concentrations (LB broth and 0.1× LB broth), interspecies interactions were explored using biofilm classification schemes. There was a strong source-dependence of biofilm development formed by the monocultures, that is, a higher biofilm formation potential for strains from attached aggregates than for those from sludge flocs at both substrate concentrations. Interestingly, the results showed that total biofilm reduction was dominant in the dual-species biofilm sourced from flocs in both LB broth (67.37%) and 0.1× LB broth (64.21%), indicating high interspecific competition in mobile aggregates and the independence of substrate concentrations. However, biofilm reduction was higher (33.68%) than induction (19.37%) for the biofilms formed by surface-attached aggregates in LB broth, while the opposite trend was apparent in 0.1× LB broth, suggesting the occurrence of indeterministic processes for biofilm formation and important roles of substrate concentrations. In addition, the more closely related phylogenetic relationships of cocultures from mobile aggregates were consistent with higher competition compared with those from surface-attached aggregates. Overall, the underlying evolutionary patterns of biofilms formed from mobile aggregates consistently followed the essence of the “Red Queen Hypothesis,” while biofilms developed from surface-attached aggregates were not deterministic. This study advanced our understanding of biofilm-related treatment processes using the principles of microbial ecology.     

榕树-榕小蜂互惠合作系统中的非对称性博弈

榕树及其传粉榕小蜂是自然界中目前所知道的关系最为紧密的互利共生系统之一。随着研究的深入, 越来越多的证据发现榕树-传粉榕小蜂之间互惠合作的过程中存在着复杂的竞争和对抗关系, 例如榕树与传粉榕小蜂之间对公共资源的竞争、传粉欺骗与宿主对传粉者的惩罚、榕树与传粉小蜂之间的“军备竞赛”等。在相互竞争或者对抗关系中, 双方表现出非对称性相互作用。其非对称性关系主要表现出如下3个特征: (1)收益不对称, 即榕树(宿主)与传粉榕小蜂(共生体)之间在资源利用等方面的实力不对称; (2)榕树与传粉榕小蜂之间的信息不对称; (3)进化速率不对称。这些非对称的相互作用可能导致种群的波动、榕树与传粉榕小蜂相互适应和进化策略的变化。因此, 理解榕树与传粉榕小蜂之间的非对称交互作用有助于理解为什么合作和冲突在互利共生关系中经常能同时存在, 也将有助于解释榕树-传粉榕小蜂种间相互关系和物种的多样性。     

Rescue tree monocultures! A phylogenetic ecology approach to guide the choice of seedlings for enrichment planting in tropical monoculture plantations

Monoculture tree plantations have been preferred by farmers and companies because they maximize the production of specific products and are easier to manage, while multispecies plantations can provide multiple ecosystem services but have still been adopted at very limited scales. One potential midway to enhance the ecological contribution of monoculture plantations is to introduce native tree species in the plantation understory. We conducted phylogenetically explicit enrichment planting experiments beneath the monocultures of two tree species native to the Brazilian Atlantic Forest to assess if the evolutionary distance of each seedling species to the overstory tree explained variations in seedling performance. We planted in the understory of two replicate plantations of species Esenbeckia leiocarpa Engl. (Rutaceae; 38 and 25 years old) and Zeyheria tuberculosa (Vell) (Bignoniaceae; both replicates were 30 years old) six native tree species, ranging in their evolutionary distances to these overstory species. We assessed individual seedling survival and height at 1, 7, and 19 months after planting. We found a weak yet significant, positive correlation between seedling performance (growth and survival) and the phylogenetic distance of the planted seedling to the overstory species, which was driven by the poor performance of conspecifics. Seedlings of the same order and class as the overstory trees showed a significantly lower risk of death compared to conspecifics and to the furthest relative, Cryptocarya aschersoniana. These findings highlight that very close relatives to the overstories should be avoided when planting beneath monoculture plantations, but that knowledge on species‐specific requirements is still the most important for a successful planting.     

Compensating for climate change–induced cue‐environment mismatches: evidence for contemporary evolution of a photoperiodic reaction norm in Colias butterflies

Anthropogenic climate change alters seasonal conditions without altering photoperiod and can thus create a cue‐environment mismatch for organisms that use photoperiod as a cue for seasonal plasticity. We investigated whether evolution of the photoperiodic reaction norm has compensated for this mismatch in Colias eurytheme. This butterfly’s wing melanization has a thermoregulatory function and changes seasonally. In 1971, Hoffmann quantified how larval photoperiod determines adult wing melanization. We recreated his experiment 47 years later using a contemporary population. Comparing our results to his, we found decreased melanization at short photoperiods but no change in melanization at long photoperiods, which is consistent with the greater increase in spring than summer temperatures recorded for this region. Our study shows that evolution can help correct cue‐environment mismatches but not in the same way under all conditions. Studies of contemporary evolution may miss important changes if they focus on only a limited range of conditions.