A test of the reproductive assurance hypothesis inIpomoea hederacea: does inbreeding depression counteract the benefits of self‐pollination?

Abstract

PremiseDarwin proposed that self‐pollination in allegedly outcrossing species might act as a reproductive assurance mechanism when pollinators or mates are scarce; however, in natural populations, the benefits of selfing may be opposed by seed discounting and inbreeding depression. While empirical studies show variation among species and populations in the magnitude of reproductive assurance, little is known about the counterbalancing effects of inbreeding depression.MethodsBy comparing the female reproductive success of emasculated and open‐pollinated flowers, we assessed the reproductive assurance hypothesis in two Mexican populations of Ipomoea hederacea. In one population, we assessed temporal variation in reproductive assurance for three years. We evaluated inbreeding depression on seed production, seedling germination, and dry plant mass by contrasting self‐ and cross‐hand pollination treatments in one population for two years.ResultThe contribution of self‐pollination to female reproductive success was high and consistent between populations, but there was variation in reproductive assurance across years. Inbreeding depression was absent in the early stages of progeny development, but there was a small negative effect of inbreeding in the probability of germination and the mass of adult progeny.ConclusionsSelf‐pollination provided significant reproductive assurance in I. hederacea but this contribution was variable across time. The contribution of reproductive assurance is probably reduced by inbreeding depression in later stages of progeny development, but this counter effect was small in the study populations. This study supports the hypothesis that reproductive assurance with limited inbreeding depression is likely an important selective force in the evolution of self‐pollination in the genus Ipomoea.

Spatiotemporal variation of chasmogamy and cleistogamy in a native perennial grass: fecundity, reproductive allocation and allometry

“…Cleistogamous reproduction has traditionally been viewed as a form of reproductive assurance that provides a way for plants to mature many seeds at a low energetic cost under conditions of pollinator scarcity ( Darwin 1877 ; Kalisz et al 2004 ; Goodwillie et al 2005 ; Eckert et al 2006 ; Veena and Nampy 2019 ; Delgado-Dávila and Martén-Rodríguez 2021 ) or stressful abiotic conditions ( Campbell et al 1983 ; Schoen 1984 ; Le Corff 1993 ; Cheplick 2007 ). Indeed, the low cost of producing CL flowers and their high seed set ( Schemske 1978 ; Schoen 1984 ; Redbo-Torstensson and Berg 1995 ; Winn and Moriuchi 2009 ; Hesse and Pannell 2011 ; Veena and Nampy 2019 ; Seguí et al 2021 ), and the absence of significant inbreeding depression in many selfing species ( Culley 2000 ; Winn et al 2011 ; Ansaldi et al 2019 ; Delgado-Dávila and Martén-Rodríguez 2021 ), argues forcibly for an evolutionary advantage of CL under many conditions. Nevertheless, exclusively CL species are not known, suggesting some advantage to the additional production of CH flowers ( Oakley et al 2007 ), especially when environmental conditions vary greatly in space and time ( Schoen and Lloyd 1984 ).…”