The role of pseudo-overdominance in maintaining inbreeding depression

Classical models ignoring linkage predict that deleterious recessive mutations purge or fix within inbred populations, yet these often retain moderate to high segregating load. True overdominance generates balancing selection that sustains inbreeding depression even in inbred populations but is rare. In contrast, arrays of mildly deleterious recessives linked in repulsion may occur commonly enough to generate pseudo-overdominance and sustain segregating load. We used simulations to explore how long pseudo-overdominant regions (POD's) persist following their creation via hybridization between populations fixed for alternative mutations at linked loci. Balancing haplotype loads, tight linkage, and moderate to strong cumulative selective effects serve to maintain POD's, suggesting that POD's may most often arise and persist in low recombination regions (e.g., inversions). Selection and drift unbalance the load, eventually eliminating POD's, but this process is very slow when pseudo-overdominance is strong. Background selection across the genome accelerates the loss of weak POD's but reinforces strong POD's in inbred populations by disfavoring homozygotes. Further modeling and studies of POD dynamics within populations could help us understand how POD's affect persistence of the load and how inbred mating systems evolve.

Comparison of Aceh cow’s performance on different mating systems at BPTU HPT Indrapuri, Aceh Province, Indonesia

This research aimed to compare Aceh cow’s performance on different mating systems at BPTU HPT Indrapuri, Indonesia. This research uses 202 Aceh cows with varying systems of mating; natural mating (164 cows), and artificial insemination (AI; 38 cows). Cow’s performance data included birth weight, postpartum mating, calving interval, weaning weight, Cow Reproduction Index (CRI), and Cow Production Index (CPI), obtained from the recording in 2014-2019 and calculation. This research uses the Oneway Anova test to analyze the cow’s performance between mating systems. The results of the cow’s performance included birth weight, postpartum mating, calving interval, weaning weight, CRI, and CPI for natural mating system were 14.32±1.41 kg, 265.61±260.0 days, 558,.21±260.07 days, 54.32±19.32 kg, 0.69 calf/cow/year and 37,48 kg/cow/year respectively, while for AI system were 14,98±1,38 kg, 289.34±285,.06 days, 581.94±285.06 days, 59.10±21.83 kg, 0.70 calf/cow/year dan 41.37 kg/kg/cow/year. The results showed that the performance of the Aceh cows with natural mating dan artificial insemination was relatively the same.

PSXI-24 Evaluation of Barbados Blackbelly and St. Croix hair sheep under accelerated lambing using purebred and terminal sire mating: Ewe fertility, prolificacy, and productivity

Objectives were to evaluate ewe performance under an accelerated, pasture-lambing system. Barbados Blackbelly (n = 85) and St. Croix ewes (n = 91) were exposed to rams of their own breed (pure) or Dorset (terminal) in November (2012 and 2014), July (2013 and 2015), and March (2014 and 2016). Traits considered were fertility (i.e., ewes lambing/ewes exposed; n = 670) and number of lambs born (NLB), number of lambs weaned (NLW), and total 65 d adjusted litter weaning weight (LWW; n = 548 each). Data were analyzed with fixed effects of ewe age (1, 1.5, 2 yr, or ≥ 2.5 yr), breed, mating system (pure vs terminal), mating month-year, and the mating system x mating month-year interaction and a random ewe effect. Fertility was greater for Barbados Blackbelly than St. Croix ewes (0.88 vs 0.73; P < 0.01) but ewe breed did not affect any other trait (P ≥ 0.06). The mating system x mating month-year interaction effect impacted all traits (P ≤ 0.03) except NLB (P = 0.09) and performance between mating systems was compared within mating month. Fertility was greater for pure than terminal mated ewes in November (0.96 vs 0.85) and July (0.94 vs 0.53; P ≤ 0.01). Following July mating, both NLB and NLW were greater for pure than terminal mated ewes (1.69 vs 1.37 lambs and 1.43 vs 1.11 lambs, respectively; P < 0.01). However, LWW was greater for terminal than pure mated ewes after November (18.0 vs 15.7 kg) and March mating (18.1 vs 14.2 kg; P ≤ 0.02). Using a terminal sire in landrace hair sheep under accelerated mating generally reduced fertility, NLB, and NLW but improved LWW. The strategic use of terminal sire mating should be considered just during breeding season, or the use of alternative sire breeds should be evaluated.

Against the Odds: Hybrid Zones between Mangrove Killifish Species with Different Mating Systems

Different mating systems are expected to affect the extent and direction of hybridization. Due to the different levels of sexual conflict, the weak inbreeder/strong outbreeder (WISO) hypothesis predicts that gametes from self-incompatible (SI) species should outcompete gametes from self-compatible (SC) ones. However, other factors such as timing of selfing and unilateral incompatibilities may also play a role on the direction of hybridization. In addition, differential mating opportunities provided by different mating systems are also expected to affect the direction of introgression in hybrid zones involving outcrossers and selfers. Here, we explored these hypotheses with a unique case of recent hybridization between two mangrove killifish species with different mating systems, Kryptolebias ocellatus (obligately outcrossing) and K. hermaphroditus (predominantly self-fertilizing) in two hybrid zones in southeast Brazil. Hybridization rates were relatively high (~20%), representing the first example of natural hybridization between species with different mating systems in vertebrates. All F1 individuals were sired by the selfing species. Backcrossing was small, but mostly asymmetrical with the SI parental species, suggesting pattern commonly observed in plant hybrid zones with different mating systems. Our findings shed light on how contrasting mating systems may affect the direction and extent of gene flow between sympatric species, ultimately affecting the evolution and maintenance of hybrid zones.

The effect of mating complexity on gene drive dynamics

Gene drive technology is being presented as a means to deliver on some of the global challenges humanity faces today in healthcare, agriculture and conservation. However, there is a limited understanding of the consequences of releasing self-perpetuating transgenic organisms into the wild populations under complex ecological conditions. In this study, we analyze the impact of three factors, mate-choice, mating systems and spatial mating network, on the population dynamics for two distinct classes of modification gene drive systems; distortion and viability-based ones. All three factors had a high impact on the modelling outcome. First, we demonstrate that distortion based gene drives appear to be more robust against the mate-choice than viability-based gene drives. Second, we find that gene drive spread is much faster for higher degrees of polygamy. With fitness cost, speed is the highest for intermediate levels of polygamy. Finally, the spread of gene drive is faster and more effective when the individuals have fewer connections in a spatial mating network. Our results highlight the need to include mating complexities while modelling the population-level spread of gene drives. This will enable a more confident prediction of release thresholds, timescales and consequences of gene drive in populations.

Maximizing genetic representation in seed collections from populations of self and cross-pollinated banana wild relatives

Background Conservation of plant genetic resources, including the wild relatives of crops, plays an important and well recognised role in addressing some of the key challenges faced by humanity and the planet including ending hunger and biodiversity loss. However, the genetic diversity and representativeness of ex situ collections, especially that contained in seed collections, is often unknown. This limits meaningful assessments against conservation targets, impairs targeting of future collecting and limits their use. We assessed genetic representation of seed collections compared to source populations for three wild relatives of bananas and plantains. Focal species and sampling regions were M. acuminata subsp. banksii (Papua New Guinea), M. balbisiana (Viet Nam) and M. maclayi s.l. (Bougainville, Papua New Guinea). We sequenced 445 samples using suites of 16–20 existing and newly developed taxon-specific polymorphic microsatellite markers. Samples of each species were from five populations in a region; 15 leaf samples from different individuals and 16 seed samples from one infructescence (‘bunch’) were analysed for each population. Results Allelic richness of seeds compared to populations was 51, 81 and 93% (M. acuminata, M. balbisiana and M. maclayi respectively). Seed samples represented all common alleles in populations but omitted some rarer alleles. The number of collections required to achieve the 70% target of the Global Strategy for Plant Conservation was species dependent, relating to mating systems. Musa acuminata populations had low heterozygosity and diversity, indicating self-fertilization; many bunches were needed (> 15) to represent regional alleles to 70%; over 90% of the alleles from a bunch are included in only two seeds. Musa maclayi was characteristically cross-fertilizing; only three bunches were needed to represent regional alleles; within a bunch, 16 seeds represent alleles. Musa balbisiana, considered cross-fertilized, had low genetic diversity; seeds of four bunches are needed to represent regional alleles; only two seeds represent alleles in a bunch. Conclusions We demonstrate empirical measurement of representation of genetic material in seeds collections in ex situ conservation towards conservation targets. Species mating systems profoundly affected genetic representation in seed collections and therefore should be a primary consideration to maximize genetic representation. Results are applicable to sampling strategies for other wild species.