Differential grandparental investment when maternal grandmothers are living versus deceased

: Tanskanen Antti O, Helle Samuli, Danielsbacka Mirkka

Publisher: The Royal Society Publishing

: Lontoo

: 2023

: Biology Letters

: BIOLOGY LETTERS

: BIOL LETTERS

: 20230061

: 19

: 5

: 1744-9561

: 1744-957X

DOI: https://doi.org/10.1098/rsbl.2023.0061

: https://doi.org/10.1098/rsbl.2023.0061

Grandparents can increase their inclusive fitness by investing time and resources in their grandchildren. However, not all grandparents make such investments equally, and between-grandparent differences in this regard can be predicted based on paternity uncertainty, lineage and grandparents' sex. Using population-based data for English and Welsh adolescents (n = 1430), we examined whether the death of the most important grandparent (in terms of investment), the maternal grandmother (MGM), changes relative support for existing hypotheses predicting differential grandparental-investment patterns. To contrast the predictions of the grandparental investment hypotheses, we used generalized order-restricted information criterion approximation. We consequently found that, when MGMs are alive, the most-supported hypothesis is 'discriminative grandparental solicitude', which ranks grandparental investment as MGMs > maternal grandfathers (MGFs) > paternal grandmothers (PGMs) > paternal grandfathers (PGFs). However, when MGMs are deceased, the paternity uncertainty hypothesis (MGFs = PGMs > PGFs) receives the most support; this is due to increased investment by PGMs. Thus, when the heaviest investors (i.e. MGMs) are deceased, PGM investments are closer to-but do not exceed-MGF investments.