Lazo-Wasem, E. | bioRxiv Science

bioRxiv2024

Global genomics of the man-o'-war (Physalia) reveal biodiversity at the ocean surface

The open ocean is a vast, highly connected environment, and the organisms found there have been hypothesized to represent massive, well-mixed populations. Of these, the Portuguese man-o-war (Physalia) is uniquely suited to dispersal, sailing the ocean surface with a muscular crest. We tested the hypothesis of a single, panmictic Physalia population by sequencing 133 genomes, and found five distinct lineages, with multiple lines of evidence showing strong reproductive isolation despite range overlap. We then scored thousands of citizen-science photos and identified four recognizable morphologies linked to these lineages. Within lineages, we detected regionally endemic subpopulations, connected by winds and currents, and identified individual long-distance dispersal events. We find that, even in these sailing species, genetic variation is highly partitioned geographically across the open ocean. SummaryThe open ocean is a vast and highly connected environment. The organisms that live there have a significant capacity for dispersal and few geographic boundaries to separate populations. Of these, the Portuguese man-o-war or bluebottle (genus Physalia) is uniquely suited to long-distance travel, using its gas-filled float and muscular crest to catch the wind and sail the sea surface. Physalia are distributed across the globe, and like many pelagic organisms, have been hypothesized to represent a massive, well-mixed population that extends across ocean basins. We tested this hypothesis by sequencing whole genomes of 133 samples collected from waters of over a dozen countries around the globe. Our results revealed five distinct lineages, with multiple lines of evidence indicating strong reproductive isolation, despite regions of range overlap. We combined these data with an independent dataset of thousands of images of Physalia uploaded to the citizen-science website inaturalist.org, which we scored for morphological characters including sail size, tentacle arrangement, and color. From these images, we identified four recognizable morphologies, described their geographical distribution, and linked them to four of the lineages identified with genomic data. We conclude there are at least four species, three of which correspond to species proposed by scientists in the 18th and 19th centuries: P. physalis, P utriculus, and P. megalista, along with one as yet unnamed species Physalia sp. from the Tasman Sea. Within each species, we observe significant population structure, with evidence of persistent subpopulations at a regional scale, as well as evidence for individual long-distance dispersal events. Our findings indicate that, instead of one well-mixed, cosmopolitan species, there are in fact multiple Physalia species with distinct but overlapping ranges, each made up of regionally endemic subpopulations that are connected by major ocean currents and wind patterns.

zoology↗

bioRxiv2019

Spatial distribution of epibionts on olive ridley sea turtles at Playa Ostional, Costa Rica

There is a wealth of published information on the epibiont communities of sea turtles, yet many of these studies have exclusively sampled epibionts found only on the carapace. Considering that epibionts may be found on almost all body-surfaces and that it is highly plausible to expect different regions of the body to host distinct epibiont taxa, there is a need for quantitative comparative studies to investigate spatial variation in the epibiont communities of turtles. To achieve this, we measured how total epibiont abundance and biomass on olive ridley turtles Lepidochelys olivacea varies among four body-areas of the hosts (n = 30). We show that epibiont loads on olive ridleys are higher, both in terms of number and biomass, on the skin than they are on the carapace or plastron. This contrasts with previous findings for other hard-shelled sea turtles, where epibionts are usually more abundant on the carapace. Moreover, the arguably most ubiquitous epibiont taxon for other hard-shelled sea turtles, the barnacle Chelonibia spp., only occurs in relatively low numbers on olive ridleys, while the barnacles Stomatolepas elegans and Platylepas hexastylos are far more abundant. We postulate that these differences between the epibiont communities of different sea turtle taxa could indicate that the carapaces of olive ridley turtles provide a more challenging substratum for epibionts than do the hard shells of other sea turtles. In addition, we conclude that it is important to conduct full body surveys when attempting to produce a holistic qualitative or quantitative characterization of the epibiont communities of sea turtles.

zoology↗