Runs of homozygosity in Sable Island feral horses reveal the genomic consequences of inbreeding and divergence from domestic breeds.

BACKGROUND: Understanding inbreeding and its impact on fitness and evolutionary potential is fundamental to species conservation and agriculture. Long stretches of homozygous genotypes, known as runs of homozygosity (ROH), result from inbreeding and their number and length can provide useful population-level information on inbreeding characteristics and locations of signatures of selection. However, the utility of ROH for conservation is limited for natural populations where baseline data and genomic tools are lacking. Comparing ROH metrics in recently feral vs. domestic populations of well understood species like the horse could provide information on the genetic health of those populations and offer insight into how such metrics compare between managed and unmanaged populations. Here we characterized ROH, inbreeding coefficients, and ROH islands in a feral horse population from Sable Island, Canada, using ~41 000 SNPs and contrasted results with those from 33 domestic breeds to assess the impacts of isolation on ROH abundance, length, distribution, and ROH islands. RESULTS: ROH number, length, and ROH-based inbreeding coefficients (FROH) in Sable Island horses were generally greater than in domestic breeds. Short runs, which typically coalesce many generations prior, were more abundant than long runs in all populations, but run length distributions indicated more recent population bottlenecks in Sable Island horses. Nine ROH islands were detected in Sable Island horses, exhibiting very little overlap with those found in domestic breeds. Gene ontology (GO) enrichment analysis for Sable Island ROH islands revealed enrichment for genes associated with 3 clusters of biological pathways largely associated with metabolism and immune function. CONCLUSIONS: This study indicates that Sable Island horses tend to be more inbred than their domestic counterparts and that most of this inbreeding is due to historical bottlenecks and founder effects rather than recent mating between close relatives. Unique ROH islands in the Sable Island population suggest adaptation to local selective pressures and/or strong genetic drift and highlight the value of this population as a reservoir of equine genetic variation. This research illustrates how ROH analyses can be applied to gain insights into the population history, genetic health, and divergence of wild or feral populations of conservation concern.

Quantifying male harm and its divergence.

Male harm arises when traits that increase reproductive success in competition with other males also harm females as a side effect. The extent of harm depends on male and female phenotypes, both of which can diverge between populations. Within a population, harm is inferred when increased exposure to males reduces female fitness, but studies of the divergence of male harm rarely manipulate male exposure. Here, we quantify male harm and compare its magnitude between two lab populations of Drosophila serrata that were derived from a common ancestor 7 years earlier and subsequently held under conditions that minimized environmental differences. We manipulated female exposure to males in a factorial design involving all four combinations of males and females from these populations, providing insight into divergence in both sexes. Our results reveal substantial harm to females and provide stronger evidence of divergence in males than in females. Using these and other published data, we discuss conceptual issues surrounding the quantification and comparison of harm that arise because it involves a comparison of multiple quantities (e.g., female fitness under varying male exposure), and we demonstrate the increased insight that is gained by manipulating male exposure to quantify these quantities.

Not playing by the rules: Unusual patterns in the epidemiology of parasites in a natural population of feral horses (Equus caballus) on Sable Island, Canada.

Sable Island, Nova Scotia, Canada hosts one of few natural populations of feral horses (Equus caballus) never exposed to anthelmintics. Coproculture revealed cyathostomes, Strongylus equinus, S. edentatus, and S. vulgaris, with S. equinus (unusually) dominating in adult horses and cyathostomes dominating in young horses (<3 years of age). We examined 35 horses found dead in the springs of 2017 and 2018, as well as fecal samples from live horses in spring (n = 45) and summer 2018 (n = 236) using McMaster fecal flotation and Baermann larval sedimentation on fresh samples, and modified Wisconsin flotation and sucrose gradient immunofluorescent assay for Giardia and Cryptosporidium on frozen samples. Mean strongyle fecal egg counts were 666 eggs per gram (EPG) in dead horses, 689 EPG in live horses in spring, and 1105 EPG in summer; domestic horses are usually treated at counts exceeding 200 EPG. Adult horses (unusually) had patent infections with the lungworm Dictyocaulus arnfieldi and ascarids (Parascaris spp.), and in spring, dead horses had 5 times higher odds of having patent ascarid infections than live horses, likely due to malnutrition and corresponding immunodeficiency. Fecal prevalence and intensity of D. arnfieldi and Parascaris spp. were significantly higher in young horses, and in spring versus summer. A higher proportion of fecal samples were positive for strongyle and ascarid eggs using a centrifugal flotation technique on previously frozen feces, as compared to a passive flotation method on fresh feces. Eggs of the tapeworm Paranoplocephala mamillana were present in fecal samples from 28% of live, and 42% of dead, horses in spring. This research represents several new geographic records (S. edentatus, D. arnfieldi, and Eimeria leuckarti), provides insight into unusual patterns of parasite epidemiology in a nutrition-limited environment, and has conservation and biosecurity implications for this unique equine population, as well as for parasite management in domestic horses.

The purging of deleterious mutations in simple and complex mating environments.

There is a general expectation that sexual selection should align with natural selection to aid the purging of deleterious mutations, yet experiments comparing purging under monogamy versus polygamy have provided mixed results. Recent studies suggest that this may be because the simplified mating environments used in these studies reduce the benefit of sexual selection through males and hamper natural selection through females by increasing costs associated with sexual conflict. To test the effect of the physical mating environment on purging, we use experimental evolution in Drosophila melanogaster to track the frequency of four separate deleterious mutations in replicate populations that experience polygamy under either a simple or structurally complex mating arena while controlling for arena size. Consistent with past results suggesting a greater net benefit of polygamy in a complex environment, two of the mutations were purged significantly faster in this environment. The other two mutations showed no significant difference between environments.

Strained ruthenium metal-organic dyads as photocisplatin agents with dual action.

Three strained Ru(II) metal-organic dyads were prepared and characterized by NMR, mass spectrometry, and analytical HPLC to probe whether these constructs could act as multifunctional photochemotherapy (PCT) agents. The compounds incorporated the crowded 6,6'-dimethyl-2,2'-bipyridine (6,6'-dmb) ligand to impart stoichiometric photocisplatin activity, and imidazo[4,5-f] [1,10]phenanthroline (IP) appended with n thiophene units (nT; n=1-3) to add capacity for singlet oxygen sensitization. With visible light activation, each complex of the series underwent rapid and selective photoejection of 6,6'-dmb in less than 10min, with half-lives (t1/2) as short as 46.3s for [Ru(6,6'-dmb)2(IP-1T)](2+). Photo-triggered ligand loss slowed with increasing n, and was slowest for [Ru(6,6'-dmb)2(IP-3T)](2+) (t1/2=273s). This trend also held for photoadduct formation with DNA; [Ru(6,6'-dmb)2(IP-1T)](2+) produced relaxed circular DNA at the lowest concentrations. Singlet oxygen yields (ΦΔ) increased with n, whereby ΦΔ for [Ru(6,6'-dmb)2(IP-1T)](2+) was only 3%, but increased to 42% on going to [Ru(6,6'-dmb)2(IP-3T)](2+). This photosensitization process was reflected by single-strand breaks in the gel-mobility shift assays of [Ru(6,6'-dmb)2(IP-3T)](2+), but was not discernible for the other compounds. Despite different photochemical and photophysical reactivities, all of the compounds were potent phototoxic agents toward cancer cells (EC50=1-2µM) with relatively short compound-to-light intervals and moderate visible light doses. [Ru(6,6'-dmb)2(IP-3T)](2+) was exceptionally photoactive toward cancer cells at longer intervals (EC50=200nM, PI=750). Phototherapeutic margins increased with n due to decreased dark cytotoxicity for the more π-expansive complexes, making metal-organic dyad [Ru(6,6'-dmb)2(IP-3T)](2+) the best multifunctional PCT agent.

Synthetic prodigiosenes and the influence of C-ring substitution on DNA cleavage, transmembrane chloride transport and basicity.

Analogues of the tripyrrolic natural product prodigiosin bearing an additional methyl and a carbonyl group at the C-ring were synthesised and evaluated. In vitro anticancer activity screening (NCI) and the study of modes of action (copper-mediated cleavage of double-stranded DNA and transmembrane transport of chloride anions) showed that the presence of the methyl group is not detrimental to activity. Furthermore, although the presence of an ester conjugated to the prodigiosene C-ring seems to decrease both pK(a) and chloride transport efficiency compared to the natural product, these analogues still exhibit a high rate of chloride transport. All analogues exhibit good in vitro anticancer activity and reduced toxicity compared to the natural product: compare an acute systemic toxicity of 100 mg kg(-1) in mice vs. 4 mg kg(-1) for prodigiosin, pointing towards a larger therapeutic window than for the natural product.

Investigations regarding the utility of prodigiosenes to treat leukemia.

Prodigiosenes, possessing a 4-methoxypyrrolyldipyrrin skeleton, are known for their anti-cancer activity. Structural modification of the C-ring resulted in a series of prodigiosenes that displayed promising activity against leukemia cell lines during in vitro analysis against the NCI 60 cancer cell line panel. Further in vivo studies of these compounds using the zebrafish model showed persistence of anti-leukemia properties in human K562 chronic myelogenous leukemia cells.