Variation in reproductive effort, genetic diversity and mating systems across Posidonia australis seagrass meadows in Western Australia

Abstract

Background and Aims Populations at the edges of their geographical range tend to have lower genetic diversity, smaller effective population sizes and limited connectivity relative to centre of range populations. Range edge populations are also likely to be better adapted to more extreme conditions for future survival and resilience in warming environments. However, they may also be most at risk of extinction from changing climate. We compare reproductive and genetic data of the temperate seagrass, Posidonia australis Hook.f. on the west coast of Australia. Methods Measures of reproductive effort (flowering and fruit production and seed to ovule ratios) and estimates of genetic diversity and mating patterns (nuclear microsatellite DNA loci) were used to assess sexual reproduction in northern range edge (low latitude, elevated salinities, Shark Bay World Heritage Site) and centre of range (mid latitude, oceanic salinity, Perth metropolitan waters) meadows in Western Australia. Key Results Flower and fruit production were highly variable among meadows and there was no significant relationship between seed to ovule ratio and clonal diversity. However, Shark Bay meadows were two orders of magnitude less fecund than those in Perth metropolitan waters. Shark Bay meadows were characterised by significantly lower levels of genetic diversity and a mixed mating system relative to meadows in Perth metropolitan waters, which had high genetic diversity and a completely outcrossed mating system. Conclusions The combination of reproductive and genetic data showed overall lower sexual productivity in Shark Bay meadows relative to Perth metropolitan waters. The mixed mating system is likely driven by a combination of local environmental conditions and pollen limitation. These results indicate that seagrass restoration in Shark Bay may benefit from sourcing plant material from multiple reproductive meadows to increase outcrossed pollen availability and seed production for natural recruitment.

Biodiversity and phylogenetic analyses using DNA barcoding rbcL gene of seagrass from Sekotong, West Lombok, Indonesia

“…Studies on seagrass genetic diversity and genetic population have been carried out in several places, such as India (Thangaradjou and Bhatt 2018), South China Sea (Hernawan 2018), Isles of Scilly, an archipelago in England (Alotaibi et al 2019), and Western Australia (Sinclair et al 2020). The studies covered tropical and temperate seagrass.…”

The Genetic Component of Seagrass Restoration: What We Know and the Way Forwards

“…Seagrass genetic diversity tends to decrease in populations that locate at the range-edge of the species' distribution range [49,102]. This phenomenon has been suggested as the result of reduced seed production and pollen limitation [10,49] and limited connectivity of populations [111][112][113]. Range-edge populations often exhibit smaller effective population sizes, making them unsuited as donor sites [111,112,114].…”

“…This phenomenon has been suggested as the result of reduced seed production and pollen limitation [10,49] and limited connectivity of populations [111][112][113]. Range-edge populations often exhibit smaller effective population sizes, making them unsuited as donor sites [111,112,114]. Indeed, many studies have recommended that populations with large effective population sizes are the most appropriate donor sites [114].…”

“…Indeed, many studies have recommended that populations with large effective population sizes are the most appropriate donor sites [114]. These populations actually possess the genetic potential to better adapt to more extreme environmental conditions (e.g., marine heatwaves) and could be used as potential restoration materials for the future as ocean warming continues to rise [10,111]. However, these populations could also be at high risk of extinction if the speed of environmental change overrides their capacity to adapt [115].…”

“…Distribution and connectivity maps together with a priori knowledge of population structure should be integrated with the reproductive characteristics of related seagrass meadows [111,116]. For example, after studying reproductive and genetic profiles of P. australis meadows across Western Australia, Sinclair et al [111] showed flower and fruit production variability between northern range-edge meadows and center range ones, with the first showing mixed mating system and lower sexual productivity. This evidence suggests that future restoration activities may benefit from sourcing plant material from multiple reproductive meadows.…”