Desert fish populations tolerate extreme salinity change to overcome hydrological constraints

Abstract

The unstable nature of freshwater ponds in arid landscapes represent a sizable challenge for strictly aquatic organisms, such as fishes. Yet the Arabian Desert, bordering the coastline of the Red Sea, plays host to a species very well adapted to such extreme environments: the Arabian pupfish, Aphanius dispar. In this study, we estimated patterns of hydrological connectivity; population structure and stable isotope for samples of A. dispar living in small, isolated ponds of nearly-freshwater in the Arabian desert and highly saline coastal lagoons along the Red Sea. The genomic and hydrological analyses indicate that populations are largely separated by drainage origin, as fish from desert ponds appear to be transported to coastal lagoons of the Red Sea along ephemeral river systems arising from flash flood events. Further, our study indicates there is an ecological change when being washed from pond environments to coastal waters, due to a significant shift in muscle stable isotopes ratios between both groups. Considering that the genetic breaks are mostly observed between drainage origin, this study suggests that A. dispar can survive large changes in salinity and ecological regimes over small time-scales.

Thermal optima of cercarial emergence in trematodes from a marine high-temperature ecosystem, the Persian Gulf

“…The establishment and subsequent flourishment of trematodes outside their current range will depend on the presence of the host species needed to complete the life cycle. While knowledge about other intermediate hosts of the studied trematodes is limited, the first intermediate host P. cingulata of both trematode species and the second intermediate host of A. tridactyla , the fish A. dispar 40 , 41 , are both eurytherms with vast geographic distributions 34 , 58 , 59 (see the Supplementary Fig. S1 ).…”

The time course of molecular acclimation to seawater in a euryhaline fish

“…Arabian pupfish from nearly-freshwater ponds (1.5 ppt) are sporadically being flushed out to highly saline environments of the Red Sea (43 ppt) through dry riverbeds (called wadies ) by flash floods (Schunter et al, 2021), where they are able to rapidly acclimate to the new environment and establish viable populations. Comparing the gill gene expression profiles of the native populations, as well as the changes across a salinity challenge from hours to weeks post-transfer, enabled the separation between short-and longer-term osmotic stress responses, and the investigation of the processes that allow pupfish to adapt to the high salinity typical of the Red Sea environment.…”

“…The plasticity of these fish under steep increases in water salinity plays a major role in the colonization potential of this species. Remarkably, Arabian pupfish are able to survive flash flood events which likely displace them from desert oases and wash them to the sea, where they eventually establish viable populations (Schunter et al, 2021). By simulating and analysing the exposure to high salinity from near-freshwater over time, not only key processes for a successful acclimation were identified, but also the importance of their timing was uncovered.…”

“…To evaluate the natural acclimation of Arabian pupfish from near-freshwater to a large increase in salinity over a short period of time, adult Aphanius dispar from the same genetic unit (Schunter et al, 2021) were collected using a seine net from two Saudi Arabian sites, including a near-freshwater (1.45 ppt) desert pond and a highly saline Red Sea coastal lagoon (43.49 ppm; Suppl. Table 1) between November 2015 and January 2016 (Fig.…”

“…While salinity changes have been observed to influence Arabian pupfish osmotic pressure, body ion content, and gill permeability (Lotan, 1969(Lotan, , 1971, no differences in performance indicators, such as resting metabolic rate, swimming speed and activity level, were caused by up to 70 ppt increases in water salinity (Plaut, 2000). In a recent genetic connectivity study supported by hydrological mapping of the region, the coastal Red Sea populations have been found to receive migrants from the inland ponds as a result of sporadic flash flood events that wash individuals out to the sea (Schunter et al, 2021). These colonization events require considerable acclimation capacities in order to survive such a rapid and drastic change in environment, especially while coping with the abrupt increase in salinity.…”