Dispersal and population expansion in a direct developing marine snail (Littorina saxatilis) following a severe population bottleneck

Repeated evolution of reproductive isolation in a marine snail: unveiling mechanisms of speciation

“…The progress of this second step is likely to start with the appearance of an uplifted island in the form of a wave-swept cliff (an E habitat). A rafted E ecotype female from a nearby larger island is the most likely founder of this little island, and in a few generations, gives rise to a population of several thousands of snails (such as has been observed following repopulation events of small islands after a toxic algal bloom, Johannesson & Johannesson 1995). After the top of the island has emerged a few metres above mean water, the first boulder habitat becomes available.…”

“…However, after a toxic algal bloom that wiped out all snails on small islands (at distances of 0.1 -1 km from larger islands), the rate of island re-colonization was 1.5 per cent per generation ( Johannesson & Johannesson 1995). As a successful recolonization requires only one adult female (see below), migration between islands in the archipelago can be estimated to be in the region of 0.03 migrants (assuming male and female rafting to be equally frequent) per generation, that is, Nm ( 1.…”

“…Notably, founding a new population will require no more than a single mated female as she has the capacity to release a few hundred offspring that will remain in the area throughout life. (Although not all offspring survive until the adult stage, observations after the algal bloom indicated that populations of re-colonized islands expanded exponentially and returned to normal densities in a few generations (Johannesson & Johannesson 1995).) Hence, one female being successfully rafted to a new site is probably enough to establish a new population in that site, and this may explain this species being established in extremely remote places like the small and isolated island of Rockall ( Johannesson 1988).…”

“…colonization is likely to be initiated by a single mated female and a new population will expand rapidly to population sizes of 10 000 snails or more (as shown by empirical observations, Johannesson & Johannesson (1995), and by modelling, Sadedin et al (2009)). Following the initial colonization, the species probably quite rapidly colonized additional areas along the coast, a process that would possibly have been completed over some 100 years ago, assuming a step-wise pattern and Nm 0.01 between adjacent sites.…”

Ethics and economics: the case for mental healthcare

“…In terms of costs, narrow perspectives are common and may lead to an inefficient allocation of resources because the exclusion of all relevant costs may alter the conclusion of a study (Johannesson 1995). Drug company evaluations are driven by the need to convince regulatory bodies and purchasers of the benefits of their products, which generally results in a narrow focus on direct health service costs.…”