Biology subjects

Saunders, G. W.

Publications and source records attributed to Saunders, G. W..

4 recordsLinked to original sources

bioRxiv2026

The genomic basis of evolutionary stasis in the 500-million-year-old red seaweed genus Ahnfeltia

The red seaweed genus Ahnfeltia is an ancient lineage that has persisted for over 500 million years with remarkably limited diversification despite a global distribution in cold-temperate intertidal habitats. Compared to the highly diverse sister lineage, Rhodymeniophycidae, Ahnfeltia provides a unique system for investigating long-term evolutionary persistence in marine macroalgae. Here, we generated chromosome-scale genomes from five populations across three species and combined population genomics with paleogeographic niche modelling. Our results reveal remarkable genomic conservation, strong geographic isolation with limited gene flow, high homozygosity, and evidence of purifying selection. Niche projections indicate long-term stability and spatial connectivity of suitable cold-temperate habitats. These findings suggest that Ahnfeltias persistence and limited diversification are linked to genomic constraints and stable ecological niches over geological timescales. This study provides new insights into the genomic basis of evolutionary stasis in ancient marine lineages and highlights potential vulnerability to ongoing climate change affecting cold-water coastal ecosystems.

evolutionary biology↗

bioRxiv2020

Spontaneous recurrent seizures in an intra-amygdala kainate microinjection model of temporal lobe epilepsy are differentially sensitive to antiseizure drugs

The discovery and development of novel antiseizure drugs (ASDs) that are effective in controlling pharmacoresistant spontaneous recurrent seizures (SRSs) continues to represent a significant unmet clinical need. The Epilepsy Therapy Screening Program (ETSP) has undertaken efforts to address this need by adopting animal models that represent the salient features of human pharmacoresistant epilepsy and employing these models for preclinical testing of investigational ASDs. One such model that has garnered increased interest in recent years is the mouse variant of the Intra-Amygdala Kainate (IAK) microinjection model of mesial temporal lobe epilepsy (MTLE). In establishing a version of this model, several methodological variables were evaluated for their effect(s) on pertinent quantitative endpoints. Although administration of a benzodiazepine 40 minutes after kainate (KA) induced status epilepticus (SE) is commonly used to improve survival, data presented here demonstrates similar outcomes (mortality, hippocampal damage, latency periods, and 90-day SRS natural history) between mice given midazolam and those that were not. Using a version of this model that did not interrupt SE with a benzodiazepine, a 90-day natural history study was performed and survival, latency periods, SRS frequencies and durations, and SRS clustering data were quantified. Finally, an important step towards model adoption is to assess the sensitivities or resistances of SRSs to a panel of approved and clinically used ASDs. Accordingly, the following ASDs were evaluated for their effects on SRSs in these mice: phenytoin (20 mg/kg, b.i.d.), carbamazepine (30 mg/kg, t.i.d.), valproate (240 mg/kg, t.i.d.), diazepam (4 mg/kg, b.i.d.), and phenobarbital (25 and 50 mg/kg, b.i.d.). Valproate, diazepam, and phenobarbital significantly attenuated SRS frequency relative to vehicle controls at doses devoid of observable adverse behavioral effects. Only diazepam significantly increased seizure freedom. Neither phenytoin nor carbamazepine significantly altered SRS frequency or freedom under these experimental conditions. These data demonstrate that SRSs in this IAK model of MTLE are pharmacoresistant to two representative sodium channel-inhibiting ASDs (phenytoin and carbamazepine) but not to GABA receptor modulating ASDs (diazepam and phenobarbital) or a mixed-mechanism ASD (valproate). Accordingly, this model is being incorporated into the NINDS-funded ETSP testing platform for treatment resistant epilepsy. HighlightsO_LIAn intra-amygdala kainate model of TLE was evaluated for pharmacoresistant seizures C_LIO_LIAdministration of midazolam during status epilepticus did not affect mortality C_LIO_LIModel characteristics were evaluated over a 90-day natural history study C_LIO_LISpontaneous seizures were resistant to phenytoin and carbamazepine C_LIO_LISpontaneous seizures were sensitive to valproic acid, diazepam, and phenobarbital C_LI

neuroscience↗

bioRxiv2020

Population structure in Arctic marine forests is shaped by diverse recolonisation pathways and far northern glacial refugia

The Arctic is experiencing a rapid shift towards warmer regimes, calling for a need to understand levels of biodiversity and ecosystem responses to climate cycles. This study examines marine refugial locations during the Last Glacial Maximum in order to link recolonization pathways to patterns of genetic diversity in Arctic marine forests. We present genetic data for 109 species of seaweed to infer community-level patterns, and hindcast species distributions during the Last Glacial Maximum to further pinpoint likely refugial locations. Sequence data revealed contiguous populations extending from the Bering Sea to the Northwest Atlantic, with high levels of genetic diversity in the East Canadian Arctic. One fifth of the species sampled appeared restricted to Arctic waters. Hindcasted species distributions highlighted refugia in the Bering Sea, Northwest Atlantic, South Greenland, and Europe. We hypothesize that Arctic coastal systems were recolonized from many geographically disparate refugia leading to enriched diversity levels in the East Canadian Arctic, with important contributions stemming from northerly refugia likely centered along Southern Greenland. Moreover, we hypothesize these northerly refugia likely played a key role in promoting polar endemic diversity, as reflected by abundant unique population haplotypes and endemic species in the East Arctic. Significance StatementOur work challenges the existing paradigm that marine Arctic ecosystems are depauperate extensions of southerly (temperate) communities established in the wake of recent glaciation, fundamentally changing how these systems should be viewed and interpreted. We forward novel hypotheses regarding the recent history of Arctic marine systems, particularly with regards to endemism being an integral feature of Arctic biomes, and present a firm framework for future evolutionary research in this system typically viewed as "ecologically immature."

genetics↗

bioRxiv2017

Molecular Analysis of Parasites in the Choreocolacaceae (Rhodophyta) Reveals a Reduced Harveyella mirabilis Plastid Genome and Supports the Transfer of Genera to the Rhodomelaceae (Rhodophyta)

Parasitism is a life strategy that has repeatedly evolved within the Florideophyceae. Historically, the terms adelphoparasite and alloparasite have been used to distinguish parasites based on the relative phylogenetic relationship of host and parasite. However, analyses using molecular phylogenetics indicate that nearly all red algal parasites infect within their taxonomic family, and a range of relationships exist between host and parasite. To date, all investigated adelphoparasites have lost their plastid, and instead, incorporate a host derived plastid when packaging spores. In contrast, a highly reduced plastid lacking photosynthesis genes was sequenced from the alloparasite Choreocolax polysiphoniae. Here we present the complete Harveyella mirabilis plastid genome, which has also lost genes involved in photosynthesis, and a partial plastid genome from Leachiella pacifica. The H. mirabilis plastid shares more synteny with free-living red algal plastids than that of C. polysiphoniae. Phylogenetic analysis demonstrates that C. polysiphoniae, H. mirabilis, and L. pacifica form a robustly supported clade of parasites, which retain their own plastid genomes, within the Rhodomelaceae. We therefore transfer all three genera from the exclusively parasitic family, Choreocolacaceae, to the Rhodomelaceae. Additionally, we recommend applying the terms archaeplastic parasites (formerly alloparasites), and neoplastic parasites (formerly adelphoparasites) to distinguish red algal parasites using a biological framework rather than taxonomic affiliation with their hosts.

evolutionary biology↗