Sampling
To understand the genetic architecture of mitonuclear incompatibilities
we focused on two well-studied populations of Tigriopus
californicus : San Diego (SD) and Santa Cruz (SC). These
populations were suitable for a competition experiment between divergent
nuclear alleles under a fixed mitochondrial background because previous
studies have shown that: i) marked mitochondrial divergence (22.17%;
Pereira et al. 2016) has driven adaptive evolution targeting
genes functionally interacting with the mitochondria (Barreto & Burton
2013a), ii) 91% of the nuclear polymorphisms are fixed among parental
populations (Pereira et al. 2016) allowing an accurate estimation
of allelic frequencies in hybrids (Lima et al. 2019), iii) F2
hybrids show breakdown at all physiological and life history traits
known to be associated with mitonuclear incompatibilities (Ellison &
Burton 2006; a; b; Barreto & Burton 2013b; Barreto et al. 2015),
and iv) strong selection during F2 development results in significant
deviations from the expected Mendelian inheritance (Foley et al.2013; Healy & Burton 2020).
Stock populations were collected in San Diego (32◦ 44′ 41.17′′ N, 117◦
15′ 19.43′′ W) and Santa Cruz (36◦ 56′ 58.32′′ N, 122◦ 2′ 48.98′′ W).
Multiple cultures from each site were maintained in 400 mL beakers at
common garden at 20°C with a 12:12 L:D photoperiod, in filtered seawater
mixed with ground “Algae Wafers” (Kyorin Co., Himeji, Japan). Beakers
were monthly mixed to promote panmixia within populations and medium was
renewed.