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opencc-zeroApr 2020View details →

Evolutionary stasis, ecophenotypy, and environmental controls on ammonite morphology in the Late Cretaceous (Maastrichtian) Western Interior Seaway, USA

We test for the presence of evolutionary stasis in a species of Late Cretaceous ammonoid cephalopod, Hoploscaphites nicolletii, from the North American Western Interior Seaway. A comprehensive dataset of morphological traits was compiled across the entire spatial and temporal range of this species. These were analyzed in conjunction with sedimentologically and geochemically derived palaeoenvironmental conditions hypothesized to apply selective pressures. All changes in shell shape were observed to be ephemeral and reversable, that is, no unidirectional trend could be observed in any of the morphological traits analyzed. Correlations between palaeoenvironmental conditions and morphological traits suggests ecophenotypic processes were at play, however, either environmental changes were too minor and/or provided no isolating mechanism to drive speciation. These data support mechanisms of stasis such as homogenizing gene flow or stabilising selection under a fluctuating optimum (likely reflecting spatiotemporally heterogeneous palaeoenvironmental conditions). Finally, changes in shell size were not significantly associated with changes in shell-specific δ18O, despite a correlation between shell size and δ18O averaged across horizons. This suggests a mismatch in scales of geochemical sampling that supports caution when making broad interpretations based on averaged geochemical data.

publicApr 2024View details →

The genomic signatures of evolutionary stasis

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publicMay 2020View details →

Evolutionary stasis, ecophenotypy, and environmental controls on ammonite morphology in the Late Cretaceous (Maastrichtian) Western Interior Seaway, USA

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publicMay 2025View details →

Evolutionary isolation and ecological stasis in the endangered Comal springs Dryopid beetle (Stygoparnus comalensis)

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Figure 5 in Karyotype stasis but species-specific repetitive DNA patterns in Anguis lizards (Squamata: Anguidae), in the evolutionary framework of Anguiformes

Figure 5. Evolutionary trends and patterns of repeat distribution in the karyotype of Anguis and Pseudopus. The summary presents: the distribution pattern of interstitial telomeric repeats (ITRs) in macrochromosomes (red arrowheads), the presence of constitutive heterochromatin in the centromeric region of chromosome No. 2 (black arrowheads), and the number and topology of 18S rDNA sites (green signals). Phylogenetic relationships follow Gvoždík et al. (2023). Although all six species share 2n = 44 and macrochromosome morphology differs only subtly, several species-specific repeat accumulation patterns have been observed. A, The common ancestor of Anguis and Pseudopus had 10 macro- and 12 microchromosome pairs, and its metacentric chromosome No. 1 likely possessed ITRs in the centromeric region. B, Accumulation of ITRs on chromosomes Nos 2, 4, and 7, and heterochromatin on chromosome No. 2; translocation and accumulation of rDNA sites on microchromosomes in the Anguis ancestor. C, Accumulation (in A. cephallonica) or elimination (in the A. fragilis species complex ancestor) of ITRs on pair Nos 5 and 9 and of rDNA sites on one of the microchromosome pairs. An asterisk indicates two possible directions of chromosomal changes. D, Elimination of ITRs on pair No. 1 in the A. fragilis species complex ancestor. E, Elimination of ITRs on chromosomes Nos 2 and 7; elimination of heterochromatin on chromosome No. 2 in the common ancestor of A. colchica and A. graeca. F, Accumulation of ITRs on chromosome No. 3 in the ancestor of A. fragilis and A. veronensis. Anguis veronensis represents a composite ITR pattern of A. cephallonica and A. fragilis, providing support for the hypothesis of past contact between Italian and Peloponnese slow worms (Gvoždík et al. 2023), with remnants of these interactions likely persisting. An alternative hypothesis proposes a shared repeat pattern among all Anguis species, wherein the detection of ITRs depends on the repeat abundance and reveals accumulations only above the detection limit.

Figure 2 in Karyotype stasis but species-specific repetitive DNA patterns in Anguis lizards (Squamata: Anguidae), in the evolutionary framework of Anguiformes

Figure 2. Distribution of constitutive heterochromatin (first column from the less side), GC/AT-positive regions (second column), telomeres and ITRs (third column), and 18S rDNA gene clusters (fourth column) in Anguis and Pseudopus (males, UN for unknown sex). First column (A, E, I, M, Q, U): presence (full arrowhead) and absence (empty arrowhead) of centromeric heterochromatin in chromosome pair No. 2. Second column (B, F, J, N, R, V): diffused GC+ pattern in distal part of pair No. 2 (empty arrowhead) or strong signal (full arrowhead) in the telomeric region of pair No. 1. Third column (C, G, K, O, S, W): ITRs (full arrowhead). Fourth column (D, H, L, P, T, X): hybridization of 18S rDNA on three pairs of microchromosomes (full arrowheads) and additional weak signal on another microchromosome pair (empty arrowheads). Where available, females do not differ from males and are shown in Supporting Information (Fig. S3).

Figure 4 in Karyotype stasis but species-specific repetitive DNA patterns in Anguis lizards (Squamata: Anguidae), in the evolutionary framework of Anguiformes

Figure 4. Chromosome painting with Varanus komodoensis (VKO) macrochromosome probes on Anguis fragilis (AFR) and Pseudopus apodus (PAP) chromosomes. The probe identity is indicated (number and letter correspond to VKO chromosome and flow-sorted peak, respectively). Arrowheads mark the hybridization signal on the AFR (A–E) and PAP (F) homeologous chromosomes. Note that each of the probes VKO 1, 2, and 3 marks two different pairs of chromosomes, whereas the probes VKO 6 + 7 and 8 + 7 mark different arms of the same chromosome pair. The hybridization signal of the probes VKO 6 + 7 and 8 + 7 does not clearly overlap in Anguis, but it marks chromosome pair No. 7 in Pseudopus.

Figure 3 in Karyotype stasis but species-specific repetitive DNA patterns in Anguis lizards (Squamata: Anguidae), in the evolutionary framework of Anguiformes

Figure 3. Male (A, C, E, G) and female (B, D, F, H) comparative genomic hybridization in four Anguis species. Male-specific DNA is labelled with fluorescein d-UTP (green), and female-specific DNA with Cy3 d-UTP (red). The yellow regions reflect regions of accumulated repetitive elements existing in equilibrium in the male and female genomes. Slightly reddish (E, F) or greenish (G, H) regions indicate certain enrichment of the repetitive fraction in the genome of one of the individuals.

Figure 1 in Karyotype stasis but species-specific repetitive DNA patterns in Anguis lizards (Squamata: Anguidae), in the evolutionary framework of Anguiformes

Figure 1. Karyograms of Anguis and Pseudopus. Male karyograms are shown, the karyograms of A. veronensis and P. apodus are from a juvenile of unknown sex. All tested individuals including females share the karyotype of 2n = 44 consisting of 20 macrochromosomes and 24 microchromosomes. Where available, karyograms of both sexes are shown in Supporting Information Figure S1. Scale bar = 10 µm. Photos on the right, not to scale.

Figure 6 in Karyotype stasis but species-specific repetitive DNA patterns in Anguis lizards (Squamata: Anguidae), in the evolutionary framework of Anguiformes

Figure 6. Schematic illustration of the homeology of the Varanus and Anguis + Pseudopus macrochromosomes with respect to the putative toxicoferan ancestor. The simplified arrangement of the macrochromosomes of the toxicoferan ancestor follows the hypothesis of Deakin and Ezaz (2019). Based on the fission(s) leading to Varanus and Anguis, we can assume that both lizards exhibit a derived stage of macrochromosome organization rather than variants of the putative ancestral arrangement of their common anguiform ancestor. The homeology of VKO 5 and AFR 6 (red and white hatched) is tentative and requires further evidence. The colour code depicts the chromosome homeology.