A large proportion of intertidal benthic marine species have a planktonic larval stage that enables connectivity among populations, with the duration of the planktonic larval period (PLD) closely reflecting population genetic structure of these species along the Southeast Pacific coast. Species with direct or short planktonic development exhibit genetic structure coinciding with major biogeographic breaks, whereas species with long planktonic development show no differentiation. Species with intermediate development have been less studied. In this study, we examined the population genetic structure of Petrolisthes violaceus along the Chilean coast, which exhibits intermediate PLD. We analyzed samples collected from eight sites between 2023 and 2024, spanning from 20°S to 42°S (approximately 2500 km). A total of 5443 Single Nucleotide Polymorphisms (SNPs) from 165 individuals were analyzed. Our results suggest the presence of two genetically differentiated populations: a northern population extending from Iquique (20°S) to Viña del Mar (33°S), and a southern population ranging from Tomé (36.6°S) to Ancud (41.8°S). Connectivity analyses revealed high gene flow among sites within each population, and biophysical model experiments revealed different dispersal patterns in the two populations. Along the Chilean coast, species with larval development lasting > 6 weeks typically exhibit no spatial population genetic structure, whereas species with abbreviated development (< 2 weeks) tend to display several genetic populations along the coast. Consistent with this pattern, P. violaceus, with an intermediate PLD of approximately 25 days, exhibits genetic differentiation in its population, with a northern and southern population spanning approximately 1400 km and 590 km, respectively.
