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Oceans cover more than 70% of the Earth’s surface and house a dizzying array of organisms. Mammals, birds, and all manner of fish can be commonly sighted at sea, but insects, the world’s most common animals, seem to be completely absent. Appearances can deceive, however, as 5 species of the ocean skater Halobates live exclusively at the ocean surface. Discovered 200 years ago, these peppercorn-sized insects remain rather mysterious. How do they cope with life at the ocean surface, and why are they the only genus of insects to have taken to the high seas?

Despite the remarkable evolutionary success of insects at colonizing every conceivable terrestrial and aquatic habitat, only five Halobates (Heteroptera: Gerridae) species (~0.0001% of all known insect species) have succeeded at colonizing the open ocean – the largest biome on Earth. This remarkable evolutionary achievement likely required unique adaptations for them to survive and thrive in the challenging oceanic environment. For the first time, we explore the morphology and behavior of an open-ocean Halobates germanus and a related coastal species H. hayanus to understand mechanisms of these adaptations. We provide direct experimental evidence based on high-speed videos which reveal that Halobates exploit their specialized and self-groomed body hair to achieve extreme water repellence, which facilitates rapid skating and plastron respiration under water. Moreover, the grooming behavior and presence of cuticular wax aids in the maintenance of superhydrophobicity. Further, reductions of their body mass and size enable them to achieve impressive accelerations (~400 ms −2 ) and reaction times (~12 ms) to escape approaching predators or environmental threats and are crucial to their survival under harsh marine conditions. These findings might also inspire rational strategies for developing liquid-repellent surfaces for drag reduction, water desalination, and preventing bio-fouling.

Relatively few insects have invaded the marine environment, and only five species of sea skaters Halobates (Hemiptera: Gerridae), have successfully colonized the surface of the open ocean. All five species occur in the Pacific Ocean, H. germanus White also occurs in the Indian Ocean, whereas H. micans Eschscholtz is the only species found in the Atlantic Ocean. We sequenced a 780 bp long region of the mitochondrial cytochrome oxidase subunit I gene (COI) for a total of 66 specimens of the five oceanic Halobates species. Our purpose was to investigate the genetic variation within species and estimate the amount of gene flow between populations. We defined 27 haplotypes for H. micans and found that haplotype lineages from each of the major oceans occupied by this species are significantly different, having sequences containing five to seven unique base substitutions. We conclude that gene flow between populations of H. micans inhabiting the Atlantic, Pacific, and Indian Ocean is limited and hypothesize that these populations have been separated for 1 to 3 million years. Similarly, there may be limited gene flow between H. germanus populations found in the Pacific and Indian Ocean and between H. sericeus populations inhabiting the northern and southern parts of the Pacific Ocean. Finally, we discuss our findings in relation to recent hypotheses about the influence of oceanic diffusion on the distribution and population structure of oceanic Halobates.

Five species of the marine insect Halobates share similar ecology but have distinct biogeographic ranges in the eastern tropical Pacific, a region from approximately 75°W–160°W and 10°S–35°N. Between 2001 and 2010, the Sea Education Association collected Halobates from 682 neuston tows (surface net 1 m × 0.5 m, 335-μm mesh) during fifteen cruises between San Diego, USA, Mexico and Tahiti. Total Halobates spp. densities varied substantially from year to year, but our data do not show a sustained change from a data set collected 40 years earlier from 1967 to 1968 (Cheng and Shulenberger in Fish Bull 78(3):579–591, 1980 ). Halobates are sensitive to sea surface temperature and we observed significant differences in species distributions over time, but these were not due to differences in water temperature or climate change. Our analyses show that the patterns observed are attributable to substantial but previously undescribed seasonal shifts that occur each year in the ranges for both Halobates sobrinus and Halobates micans . There is substantial overlap in ranges during seasonal shifts, but very little co-occurrence of H. sobrinus and H. micans in individual net tows, suggesting biological mechanisms rather than physical factors are restricting distribution and co-occurrence of these two species.

A series of studies were conducted during two cruises between Tokyo and Honolulu in September 2010 and from February to March 2012. The aims of the studies were to (1) compare the distribution of three species of Halobates oceanic skaters, H. germanus, H. micans, and H. sericeus, with respect to their temperature limits; (2) identify the lower temperature limit of H. sericeus, the species that displays the widest distribution range (40°N–35°S) latitude; and (3) test the hypothesis that H. sericeus can change their temperature tolerance to adapt to seasonal changes in sea surface temperatures. The heat coma temperature (HCT) was measured during the two cruises and the values were compared between the two populations of H. sericeus. The species collected in September 2010 were H. germanus, H. micans, and H. sericeus. H. sericeus was dominant, occupying more than 90% of the collecting sites. H. germanus and H. micans were collected in the northern and western part of the cruise track (29–34°N, 141–151°E), and not in the southern and eastern part. The population density of these two species was 9000–150,000/km2 in the first cruise, which took place in summer. On the other hand, H. sericeus was collected throughout the cruise track during that cruise. The population density of H. sericeus was relatively high, at 4000–310,000/km2, in the southern and eastern part of the cruise track (19–29°N, 152°E–165°W). In February and March 2012, only H. sericeus was collected at a density of 17,000–80,000/km2 and only in the eastern and southern part, at 25°–28°N, 169°E–178°W. No Halobates oceanic skaters were found in the western or northern part (30°N and further north, 159°E and further west) during that cruise. The lower limit for the inhabitation of sea surface temperatures appeared to be 27.8 °C or slightly lower for H. germanus and H. micans, but was 22.1 °C or slightly lower for H. sericeus. H. sericeus specimens, mostly adults, that had been collected during the two cruises were used in heat coma experiments. Summer specimens showed significantly higher heat coma temperatures (HCTs) than the winter specimens. This difference in HCTs may be the result of relatively long term temperature acclimation in the summer or winter for the adults that inhabit the temperate and subtropical areas along the cruise tracks between Tokyo and Honolulu in the Pacific Ocean. This temperature plasticity of H. sericeus may be related to the wider latitude area inhabited by this species (main range: 40°N–25°S).

The oceans are harsh environments where insects are not expected to thrive, yet a few skaters of the genus Halobates Eschscholtz, 1822 (Hemiptera: Heteroptera: Gerridae) have completely adapted to life on the open seas. There are five oceanic Halobates species that have well-established and distinct distributions, but little is known about their population dynamics and intraspecific genetic variation. Moreover, existing knowledge on most species has been largely based on limited sample sizes. We examined the phylogeographic patterns and inferred past population dynamics of three Halobates species (H. micans Eschscholtz, 1822, H. sobrinus White, 1883 and H. splendens Witlaczil, 1886) based on an unprecedented large number of specimens (73–199 individuals each) collected from the Eastern Tropical Pacific (ETP) Ocean. These species have distinct biogeographies, with H. sobrinus occurring mostly along coastal Mexico, H. micans in the ETP north of the equator, and H. splendens largely south of the equator in the cold tongue of water derived from the Peru (Humboldt) current. We did not find evidence for sub-population structure within each species over distances as far as 6000–7000 km. Populations of all three species were found to deviate from neutrality, with evidence of past population growth. Genetic diversity and haplotype genealogies varied between species, implying distinct evolutionary trajectories. Coalescent analyses using Bayesian skyline plots suggested that H. splendens underwent a population expansion ~ 1 Ma, whereas H. sobrinus and H. micans experienced demographic growth ~ 120 Ka to 100 Ka, respectively. The period of population expansion of H. splendens roughly corresponds to the establishment of cool, productive waters in the cold tongue starting ~ 1 Ma and reaching modern temperatures ~ 800 Ka. Population expansions of both H. micans and H. sobrinus north of the equator occurred mostly during the last interglacial period, characterized by increased frequency and dominance of El Niño conditions, and a relatively southerly position of the Intertropical Convergence Zone of high rainfall. Intensification of El Niño conditions between ~ 75 and 125 Ka may have produced a warmer, low wind and nutrient-depleted habitat favoring population growth for both H. micans and H. sobrinus. Key insights drawn from the results of this study, alongside future resolution of evolutionary relationships among Halobates species, will complete our understanding of how these remarkable insects conquered the high seas where no other insect could.

Temperature acclimation and heat shock experiments were performed on adult oceanic skaters, Halobates germanus, inhabiting the tropical Pacific Ocean. Acclimation for 10 or 24 h to 25 °C or 28 °C promoted significantly lower cool coma temperatures by specimens than acclimation to 31 °C. After heat shock by exposure to the relatively moderate temperature of 32.5 °C for 12 h, 52.9% or 61.1%% of specimens died in the 24 h period following acclimation at 28 °C or 31 °C, respectively, whereas all survived when there was no experience of heat shock. The average cool coma temperature was 14 to 17 °C in the specimens which had suffered no heat shock, whereas it was much higher (22 to 23 °C) in specimens that had suffered heat shock. The lower survival rate and the higher cool coma temperature can be attributed to damage suffered by exposure to 32.5 °C. The upper limit of the surface water temperature in the tropical ocean (15° N to 15° S) is currently around 30 to 31 °C, and Halobates appear to have no experience in 32 to 33 °C environments. Nevertheless, 32 °C, i.e., a temperaturethat is only slightly higher than 30 to 31 °C, may occur in the future due to global warming. This species may develop resistance to 32 to 33 °C in the near future.

Background Halobates , commonly known as sea skaters, are predatory Hemipterans uniquely adapted to tropical marine environments. Their ability to thrive in oligotrophic and environmentally extreme habitats, such as the open ocean surface and marine coastal areas, suggests the evolution of specialised adaptations, possibly including symbiotic associations with microorganisms that can support nutrition, niche adaptation, and stress resilience. To explore this hypothesis, we analysed the bacterial communities associated with Halobates melleus , a species inhabiting the Red Sea coastal mangroves in Saudi Arabia. Results Amplicon sequencing of the 16S rRNA gene and metagenomic analyses of composite body and gut samples from adult H. melleus revealed a population-level bacterial community dominated by Wolbachia and Spiroplasma , consistent with patterns observed in several terrestrial predatory insects. Members of Providencia and Swaminathania were also detected, along with other minor taxa that may represent transient environmental commensals. The identified bacteria encoded genes for the biosynthesis of essential vitamins and prosthetic groups, such as riboflavin and heme—compounds typically not synthesised de novo by insects—as well as amino acids, likely contributing to the host’s nutritional requirements. Notably, the Wolbachia metagenome-assembled genome from H. melleus clustered within the supergroup B, showing high genetic similarity to strains from phylogenetically distant Dipteran and Lepidopteran hosts that nonetheless inhabit common ecological niches, i.e., mangrove and tropical environments. This extends the known ecological breadth of Wolbachia symbioses to marine insects, underscoring their evolutionary and environmental versatility. Conclusion Our findings highlight the potential nutritional and metabolic roles of the Halobates -associated bacterial microbiome, particularly members of the Wolbachia genus. This emphasises the importance of microbial symbionts in the ecological success and adaptation of marine insects, offering a perspective complementary to previously studied terrestrial insect microbiomes.

This study, conducted during a scientific cruise, MR15-04, aims, first, to examine species and larval/adult components of Halobates (Heteroptera: Gerridae) inhabiting the tropical Indian Ocean of 4°00′ S–7°00′ S, 101°00′ E–103°00′ E and, second, to examine the correlative relationship between precipitation just before collection and the number of sea skaters collected in November and December 2015. Near Sumatra (50 km south-west), larvae and adults of four species of Halobates (Halobates germanes White, 1883; Halobates micans Eschscholtz, 1822; Halobates princeps White, 1883; undescribed species: Halobates sp.) were collected. Adults of an undescribed species had about a 5 mm long body in a gourd-like shape. One male adult specimen of H. princeps was collected. Body length, body width, and head width was measured in all specimens of Halobates. Six larval stages were detected in all three species of sea skaters as the first finding for Heteropteran insects. There was a negative correlation between amount of precipitation for 19 h before collection and the number of Halobates individuals collected by the neuston net. Death or (positive or passive) sinking by sea skaters could be due to occasional rain fall on the sea surface.

The buoyancy properties of anthropogenic microparticles (AM) have contributed to their wide dispersion across rivers and oceans, as they tend to float and can be transported by wind and marine currents. The aim of this study was to evaluate the abundance and distribution of AM in relation to zooplankton abundance in three coastal localities from the southern Mexican Pacific. Thirty-nine zooplankton samples were collected along eleven transects perpendicular to the coast of Oaxaca; in three localities: Puerto Escondido, Huatulco, and Salina Cruz, from April 30 to May 12, 2017- Sixty-eight percent of samples showed evidence of AM (mainly microfibers), with abundances varying by locations between 0.004 to 8.72 microparticles per 1000 m 3 . The relationship between zooplankton biomass and AM abundance was not statistically significant ( r 2  = 0.0104), likely due to the dispersion of AM towards the open ocean by offshore winds that reduce coastal concentrations.