Phylogeographic patterns in the Philippine archipelago influence symbiont diversity in the bobtail squid–Vibrio mutualism

Abstract

Marine microbes encounter a myriad of biotic and abiotic factors that can impact fitness by limiting their range and capacity to move between habitats. This is especially true for environmentally transmitted bacteria that cycle between their hosts and the surrounding habitat. As geologic history, biogeography, and other factors such as water temperature, salinity, and physical barriers can inhibit bacterial movement to novel environments, we chose to examine the genetic architecture of Euprymna albatrossae (Mollusca: Cephalopoda) and their Vibrio fischeri symbionts in the Philippine archipelago using a combined phylogeographic approach. Eleven separate sites in the Philippine islands were examined using haplotype estimates that were examined via nested clade analysis to determine the relationship between E. albatrossae and V. fischeri populations and their geographic location. Identical analyses of molecular variance (AMOVA) were used to estimate variation within and between populations for host and symbiont genetic data. Host animals demonstrated a significant amount of variation within island groups, while symbiont variation was found within individual populations. Nested clade phylogenetic analysis revealed that hosts and symbionts may have colonized this area at different times, with a sudden change in habitat. Additionally, host data indicate restricted gene flow, whereas symbionts show range expansion, followed by periodic restriction to genetic flow. These differences between host and symbiont networks indicate that factors “outside the squid” influence distribution of Philippine V. fischeri. Our results shed light on how geography and changing environmental factors can impact marine symbiotic associations at both local and global scales.

New bobtail squid (Sepiolidae: Sepiolinae) from the Ryukyu islands revealed by molecular and morphological analysis

“…More than a century of classical morphology-based taxonomy has more recently been augmented by surveys of the mitochondrial cytochrome oxidase I (COI) marker in bobtail squids 27–36 , especially in the subfamily Sepiolinae. While COI molecular characters (i.e., variable sites) supplement morphological features in this taxonomically tricky group of cephalopods, several misidentifications have been reported for the North Sea Sepiola species after COI sequencing and morphological analysis 37 .…”

Strain-level diversity of symbiont communities between individuals and populations of a bioluminescent fish

“…This could be due to ecological processes that influence which symbiont genotypes are available to larval fish hosts in each location during the window of colonization or alternatively, it could be a reflection of local host preference for native symbiont strains. Studies of the luminous symbionts of sepiolid squids over fairly large geographic scales showed a competitive advantage of native symbiont strains in colonizing E. scolopes light organs [49,50]. Future studies determining whether S. tubifer hosts can discriminate between local and "foreign" symbionts would provide more insight into the processes structuring these geographically distinct symbiont communities.…”

Environmental Stress Selects for Innovations That Drive Vibrio Symbiont Diversity

“…Vibrio bacteria have been observed in a wide range of habitats that vary in temperature, creating conditions that select for specific phenotypes that can survive and proliferate, both in their free-living mode as well as in their symbiotic lifestyle (Kimbell et al, 2002;Soto et al, 2009). Most notably, populations can vary, particularly when there are specific temperature gradients commonly found in nature (Jones et al, 2006;Coryell et al, 2018). For example, when sampling populations of Euprymna tasmanica, the sepiolid host squid for Vibrio fischeri in Australia, a distinct population break occurs within the symbionts where the habitat changes, particularly due to currents from the south (colder) and those from the north (warmer; Jones et al, 2006).…”

“…For example, when sampling populations of Euprymna tasmanica, the sepiolid host squid for Vibrio fischeri in Australia, a distinct population break occurs within the symbionts where the habitat changes, particularly due to currents from the south (colder) and those from the north (warmer; Jones et al, 2006). This can also be observed in environments that have seasonal changes in water temperature, or those driven by currents (Coryell et al, 2018). Interestingly, when vibrio bacteria are "forced" into specific temperature regimes, they can rapidly adapt to survival outside the host, which oftentimes promotes the coevolution between hosts and their symbionts (Cohen et al, 2019).…”