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Phytoliths are opal silica particles formed within plant tis- sues. Diatoms are aquatic, single-celled photosynthetic algae with silica skeletons. Phytolith and diatom morphotypes vary depending on local environmental and climatic conditions and because their silicate structures preserve well, the study of phytolith and diatom morphotypes can be used to better understand paleoclimatic and paleoenvironmental dynam- ics and changes. This article presents original data from an 820cm-deep stratigraphy excavated at the Hazen diatomite deposits, a high-elevation desert paleolake in the Fernley Dis- trict, Northern Nevada, USA. The site has been studied for an assemblage of fossilized threespine stickleback, Gasterosteus doryssus , that reveal adaptive evolution. For this study, a to- tal of 157 samples were extracted at 20 cm intervals cover- ing approximately 24,500 years. After extraction, the samples were mounted on slides and viewed under 40 0-10 0 0x light microscopy, enabling classification of 14 phytolith and 45 di- atom morphotypes. Our data support paleoenvironmental re- constructions of the Hazen Miocene paleolake. ∗ 

Abstract An evolutionary debate contrasts the importance of genetic convergence versus genetic redundancy. In genetic convergence, the same adaptive trait evolves because of similar genetic changes. In genetic redundancy, the adaptive trait evolves using different genetic combinations, and populations might not share the same genetic changes. Here we address this debate by examining single nucleotide polymorphisms (SNPs) associated with the rapid evolution of character displacement in Anolis carolinensis populations inhabiting replicate islands with and without a competitor species (1Spp and 2Spp islands, respectively). We identify 215-outliers SNPs that have improbably large FST values, low nucleotide variation, greater linkage than expected and that are enriched for genes underlying animal movement. The pattern of SNP divergence between 1Spp and 2Spp populations supports both genetic convergence and genetic redundancy for character displacement. In support of genetic convergence: all 215-outliers SNPs are shared among at least three of the five 2Spp island populations, and 23% of outlier SNPS are shared among all five 2Spp island populations. In contrast, in support of genetic redundancy: many outlier SNPs only have meaningful allele frequency differences between 1Spp and 2Spp islands on a few 2Spp islands. That is, on at least one of the 2Spp islands, 77% of outlier SNPs have allele frequencies more similar to those on 1Spp islands than to those on 2Spp islands. Focusing on genetic convergence is scientifically rigorous because it relies on replication. Yet, this focus distracts from the possibility that there are multiple, redundant genetic solutions that enhance the rate and stability of adaptive change. 

Recent studies have shown that the repeated evolution of similar phenotypes in response to similar ecological conditions (here “parallel evolution”) often occurs through mutations in the same genes. However, many previous studies have focused on known candidate genes in a limited number of systems. Thus, the question of how often parallel phenotypic evolution is due to parallel genetic changes remains open. Here, we used quantitative trait locus (QTL) mapping in F2 intercrosses between lake and stream threespine stickleback (Gasterosteus aculeatus) from four independent watersheds on Vancouver Island, Canada to determine whether the same QTL underlie divergence in the same phenotypes across, between, and within watersheds. We find few parallel QTL, even in independent crosses from the same watershed or for phenotypes that have diverged in parallel. These findings suggest that different mutations can lead to similar phenotypes. The low genetic repeatability observed in these lake-stream systems contrasts with the higher genetic repeatability observed in other stickleback systems. We speculate that differences in evolutionary history, gene flow, and/or the strength and direction of selection might explain these differences in genetic parallelism and emphasize that more work is needed to move beyond documenting genetic parallelism to identifying the underlying causes.

 

Loss and reduction in paired appendages are common in vertebrate evolution. How often does such convergent evolution depend on similar developmental and genetic pathways? For example, many populations of the threespine stickleback and ninespine stickleback (Gasterosteidae) have independently evolved pelvic reduction, usually based on independent mutations that caused reducedPitx1expression. ReducedPitx1expression has also been implicated in pelvic reduction in manatees. Thus, hindlimb reduction stemming from reducedPitx1expression has arisen independently in groups that diverged tens to hundreds of millions of years ago, suggesting a potential for repeated use ofPitx1across vertebrates. Notably, hindlimb reduction based on the reduction inPitx1expression produces left‐larger directional asymmetry in the vestiges. We used this phenotypic signature as a genetic proxy, testing for hindlimb directional asymmetry in six genera of squamate reptiles that independently evolved hindlimb reduction and for which genetic and developmental tools are not yet developed:Agamodon anguliceps,Bachia intermedia,Chalcides sepsoides,Indotyphlops braminus,Ophisaurus attenuatuas and O. ventralis, andTeius teyou. Significant asymmetry occurred in one taxon,Chalcides sepsoides, whose left‐side pelvis and femur vestiges were 18% and 64% larger than right‐side vestiges, respectively, suggesting modification inPitx1expression in that species.However, there was either right‐larger asymmetry or no directional asymmetry in the other five taxa, suggesting multiple developmental genetic pathways to hindlimb reduction in squamates and the vertebrates more generally.

 

Recent methodological advances have led to a rapid expansion of evolutionary studies employing three‐dimensional landmark‐based geometric morphometrics (GM). GM methods generally enable researchers to capture and compare complex shape phenotypes, and to quantify their relationship to environmental gradients. However, some recent studies have shown that the common, inexpensive, and relatively rapid two‐dimensional GM methods can distort important information and produce misleading results because they cannot capture variation in the depth (Z) dimension. We use micro‐CT scanned threespine stickleback (Gasterosteus aculeatusLinnaeus, 1758) from six parapatric lake‐stream populations on Vancouver Island, British Columbia, to test whether the loss of the depth dimension in 2D GM studies results in misleading interpretations of parallel evolution. Using joint locations described with 2D or 3D landmarks, we compare results from separate 2D and 3D shape spaces, from a combined 2D‐3D shape space, and from estimates of biomechanical function. We show that, although shape is distorted enough in 2D projections to strongly influence the interpretation of morphological parallelism, estimates of biomechanical function are relatively robust to the loss of the Z dimension.