Assessing inbreeding depression in experimental mating of annual and perennial kelp

The challenges of population persistence in annual and perennial species have lead to hypotheses for different selfing rates among species.  One hypothesis is that annuals may self more often than perennials for reproductive assurance.  Among perennials, a longer generation time may lead to an accumulation of harmful mutations in the population, suggesting increased inbreeding depression as a result of selfing and thus selection against high selfing rates.  Here I compare inbreeding depression between several species of annual and perennial kelp having mixed mating systems and an inconspicuous or absent seed bank.  This experiment analyzed juvenile survivorship under three levels of selfing probability, 5%, 50% and 100% selfing and compared the reduction in offspring from the mostly outcrossing treatment to the entirely selfed treatment.  Although all species selfed, perennials suffered the highest mortality in the selfing treatment as compared to the outcrossing treatment, while annuals either did not differ or differed very little in survivorship between selfing and outcrossing.  The results suggest that annual species may suffer fewer costs of selfing compared with annuals and supports the idea that longevity may lead to differences in mating systems.