Experimental evolution in the cyanobacterium Trichormus variabilis: increases in size and morphological diversity.

Cyanobacteria morphology has apparently remained almost unchanged for billions of years, exhibiting remarkable evolutionary stasis. Cyanobacteria appear to have reached their maximum morphological complexity in terms of size, modes of multicellularity, and cellular types by ~2 Ga. This contrasts with the increased complexity observed in other multicellular lineages, such as plants. Using experimental evolution, we show that morphological diversity can rapidly evolve in a species of filamentous cyanobacteria. Since size has such significance with regard to organismal complexity, we subjected the heterocyst-forming cyanobacterium Trichornus variabilis (syn. Anabaena variabilis) to selection for larger size. We observed increases in size of more than 30-fold, relative to the ancestral population, after 45 cycles of selection. Two distinguishable nascent morphological elaborations were identified in all the selected populations: Tangle (long, tangled filaments) and Cluster (clusters of short filaments) morphology. Growth from single cells indicates heritability of the evolved Tangle and Cluster morphological phenotypes. Cyanobacteria evolutionary conservatism is ascribed to developmental constraints, slow evolution rates, or ecological flexibility. These results open opportunities to study possibilities and constraints for the evolution of higher integrated biological levels of organization within this lineage.

Maternal effects do not resolve the paradox of stasis in birth weight in a wild red deer populaton.

In natural populations, quantitative traits seldom show short-term evolution at the rate predicted by evolutionary models. Resolving this "paradox of stasis" is a key goal in evolutionary biology, as it directly challenges our capacity to predict evolutionary change. One particularly promising hypothesis to explain the lack of evolutionary responses in a key offspring trait, body weight, is that positive selection on juveniles is counterbalanced by selection against maternal investment in offspring growth, given that reproduction is costly for the mothers. Here, we used data from one of the longest individual-based studies of a wild mammal population to test this hypothesis. We first showed that despite positive directional selection on birth weight, and heritable variation for this trait, no genetic change has been observed for birth weight over the past 47 years in the study population. Contrarily to our expectation, we found no evidence of selection against maternal investment in birth weight-if anything, selection favors mothers that produce large calves. Accordingly, we show that genetic change in birth weight over the study period is actually lower than that predicted from models including selection on maternal performance; ultimately our analysis here only deepens rather than resolves the paradox of stasis.

Social competition as a driver of phenotype-environment correlations: implications for ecology and evolution.

While it is universally recognised that environmental factors can cause phenotypic trait variation via phenotypic plasticity, the extent to which causal processes operate in the reverse direction has received less consideration. In fact individuals are often active agents in determining the environments, and hence the selective regimes, they experience. There are several important mechanisms by which this can occur, including habitat selection and niche construction, that are expected to result in phenotype-environment correlations (i.e. non-random assortment of phenotypes across heterogeneous environments). Here we highlight an additional mechanism - intraspecific competition for preferred environments - that may be widespread, and has implications for phenotypic evolution that are currently underappreciated. Under this mechanism, variation among individuals in traits determining their competitive ability leads to phenotype-environment correlation; more competitive phenotypes are able to acquire better patches. Based on a concise review of the empirical evidence we argue that competition-induced phenotype-environment correlations are likely to be common in natural populations before highlighting the major implications of this for studies of natural selection and microevolution. We focus particularly on two central issues. First, competition-induced phenotype-environment correlation leads to the expectation that positive feedback loops will amplify phenotypic and fitness variation among competing individuals. As a result of being able to acquire a better environment, winners gain more resources and even better phenotypes - at the expense of losers. The distinction between individual quality and environmental quality that is commonly made by researchers in evolutionary ecology thus becomes untenable. Second, if differences among individuals in competitive ability are underpinned by heritable traits, competition results in both genotype-environment correlations and an expectation of indirect genetic effects (IGEs) on resource-dependent life-history traits. Theory tells us that these IGEs will act as (partial) constraints, reducing the amount of genetic variance available to facilitate evolutionary adaptation. Failure to recognise this will lead to systematic overestimation of the adaptive potential of populations. To understand the importance of these issues for ecological and evolutionary processes in natural populations we therefore need to identify and quantify competition-induced phenotype-environment correlations in our study systems. We conclude that both fundamental and applied research will benefit from an improved understanding of when and how social competition causes non-random distribution of phenotypes, and genotypes, across heterogeneous environments.

Alteration of (Frequency-Dependent) Fitness in Time-Shift Experiments Reveals Cryptic Coevolution and Uncoordinated Stasis in a Virtual Jurassic Park.

Among the major unresolved questions in ecosystem evolution are whether coevolving multispecies communities are dominated more by biotic or by abiotic factors, and whether evolutionary stasis affects performance as well as ecological profile; these issues remain difficult to address experimentally. Digital evolution, a computer-based instantiation of Darwinian evolution in which short self-replicating computer programs compete, mutate, and evolve, is an excellent platform for investigating such topics in a rigorous experimental manner. We evolved model communities with ecological interdependence among community members, which were subjected to two principal types of mass extinction: a pulse extinction that killed randomly, and a selective press extinction involving an alteration of the abiotic environment to which the communities had to adapt. These treatments were applied at two different strengths (Strong and Weak), along with unperturbed Control experiments. We performed several kinds of competition experiments using simplified versions of these communities to see whether long-term stability that was implied previously by ecological and phylogenetic metrics was also reflected in performance, namely, whether fitness was static over long periods of time. Results from Control and Weak treatment communities revealed almost completely transitive evolution, while Strong treatment communities showed higher incidences of temporal intransitivity, with pre-treatment ecotypes often able to displace some of their post-recovery successors. However, pre-treatment carryovers more often had lower fitness in mixed communities than in their own fully native conditions. Replacement and invasion experiments pitting single ecotypes against pre-treatment reference communities showed that many of the invading ecotypes could measurably alter the fitnesses of one or more residents, usually with depressive effects, and that the strength of these effects increased over time even in the most stable communities. However, invaders taken from Strong treatment communities often had little or no effect on resident performance. While we detected periods of time when the fitness of a particular evolving ecotype remained static, this stasis was not permanent and never affected an entire community at once. Our results lend support to the fitness-deterioration interpretation of the Red Queen hypothesis, and highlight community context dependence in determining fitness, the shaping of communities by both biotic factors and abiotic forcing, and the illusory nature of evolutionary stasis. Our results also demonstrate the potential of digital evolution studies to illuminate many aspects of evolution in interacting multispecies communities.

Systematics, ecology and distribution of the mygalomorph spider genus Cteniza Latreille, 1829 (Araneae, Mygalomorphae, Ctenizidae).

The type-genus of the mygalomorph spider family Ctenizidae (Cteniza) is newly diagnosed and described. The type-species of Cteniza (C. sauvagesi) is reestablished by describing and designating a neotype collected at the type locality of the species, in Corsica. Alongside the female neotype, the male of C. sauvagesi is redescribed, as well as both sexes of C. moggridgei. We confirm the presence of C. sauvagesi in Sardinia and record this species for the first time in mainland Italy (Calabria) and the island of Ponza (Thyrrenian Sea). Based on our findings, Cteniza sauvagesi and C. moggridgei are diagnosed on subtle differences in their morphology. Differences between the two species in ecology and distributions are also explored by means of species distribution modeling. Finally, we amend the taxonomic status of two species whose validities have long been questionable. C. brevidens is synonymized with C. sauvagesi, and C. ferghanensis is transferred to the genus Ummidia.

Lycophyte plastid genomics: extreme variation in GC, gene and intron content and multiple inversions between a direct and inverted orientation of the rRNA repeat.

Lycophytes are a key group for understanding vascular plant evolution. Lycophyte plastomes are highly distinct, indicating a dynamic evolutionary history, but detailed evaluation is hindered by the limited availability of sequences. Eight diverse plastomes were sequenced to assess variation in structure and functional content across lycophytes. Lycopodiaceae plastomes have remained largely unchanged compared with the common ancestor of land plants, whereas plastome evolution in Isoetes and especially Selaginella is highly dynamic. Selaginella plastomes have the highest GC content and fewest genes and introns of any photosynthetic land plant. Uniquely, the canonical inverted repeat was converted into a direct repeat (DR) via large-scale inversion in some Selaginella species. Ancestral reconstruction identified additional putative transitions between an inverted and DR orientation in Selaginella and Isoetes plastomes. A DR orientation does not disrupt the activity of copy-dependent repair to suppress substitution rates within repeats. Lycophyte plastomes include the most archaic examples among vascular plants and the most reconfigured among land plants. These evolutionary trends correlate with the mitochondrial genome, suggesting shared underlying mechanisms. Copy-dependent repair for DR-localized genes indicates that recombination and gene conversion are not inhibited by the DR orientation. Gene relocation in lycophyte plastomes occurs via overlapping inversions rather than transposase/recombinase-mediated processes.

A needle in a haystack: Mesozoic origin of parasitism in Strepsiptera revealed by first definite Cretaceous primary larva (Insecta).

Twisted winged insects (Strepsiptera) are a highly specialized small order of parasitic insects. Whether parasitism developed at an early or late stage in the evolution of the group was unknown. Here we record and describe the first definite Mesozoic strepsipteran primary larva embedded in Burmese amber (∼99 million years ago). This extends the origin of parasitism back by at least ∼50 million years, and reveals that this specialized life style has evolved in the Mesozoic or even earlier in the group. The extremely small first instar displays all diagnostic characters of strepsipteran immatures of this stage and is nearly identical with those of Mengenillidae, one of the most "ancestral" extant strepsipteran taxa. This demonstrates a remarkable evolutionary stasis over  100 million years. The new finding strongly weakens the case of small larvae embedded in Cretaceous amber interpreted as strepsipteran immatures. They differ in many structural features from extant strepsipteran primary larvae and are very likely parasitic beetle larvae.

Scrophularia arguta, a widespread annual plant in the Canary Islands: a single recent colonization event or a more complex phylogeographic pattern?

Many studies have addressed evolution and phylogeography of plant taxa in oceanic islands, but have primarily focused on endemics because of the assumption that in widespread taxa the absence of morphological differentiation between island and mainland populations is due to recent colonization. In this paper, we studied the phylogeography of Scrophularia arguta, a widespread annual species, in an attempt to determine the number and spatiotemporal origins of dispersal events to Canary Islands. Four different regions, ITS and ETS from nDNA and psbA-trnH and psbJ-petA from cpDNA, were used to date divergence events within S. arguta lineages and determine the phylogenetic relationships among populations. A haplotype network was obtained to elucidate the phylogenetic relationships among haplotypes. Our results support an ancient origin of S. arguta (Miocene) with expansion and genetic differentiation in the Pliocene coinciding with the aridification of northern Africa and the formation of the Mediterranean climate. Indeed, results indicate for Canary Islands three different events of colonization, including two ancient events that probably happened in the Pliocene and have originated the genetically most divergent populations into this species and, interestingly, a recent third event of colonization of Gran Canaria from mainland instead from the closest islands (Tenerife or Fuerteventura). In spite of the great genetic divergence among populations, it has not implied any morphological variation. Our work highlights the importance of nonendemic species to the genetic richness and conservation of island flora and the significance of the island populations of widespread taxa in the global biodiversity.

Euglyphid testate amoebae (rhizaria: euglyphida) from an arctic eocene waterbody: evidence of evolutionary stasis in plate morphology for over 40 million years.

Well-preserved siliceous plates representing multiple species of euglyphids are described from a Middle Eocene maar lake deposit located near the Arctic Circle in northern Canada. Siliceous plate morphotypes including scutiform, rectangular, hexagonal, oval and circular body forms, six apertural plate types containing from five to thirteen teeth and spine plates, are documented. Many plate types bear resemblance to those found on modern species as well as ones documented from Miocene sites. These findings extend the known geological record for euglyphids and support the concept of evolutionary stasis in regards to plate morphology over much of the Cenozoic. Future use of these euglyphid remains, in conjunction with other microfossil assemblages, for reconstructing historical conditions within the maar lake is discussed.