Do s genes or deleterious recessives control late-acting self-incompatibility in Handroanthus heptaphyllus (Bignoniaceae)? A diallel study with four full sib progeny arrays

Background and Aims Genetically controlled self-incompatibility (SI) mechanisms constrain selfing and thus have contributed to the evolutionary diversity of flowering plants. In homomorphic gametophytic SI (GSI) and homomorphic sporophytic SI (SSI), genetic control is usually by a single multi-allelic locus S. Both GSI and SSI prevent self pollen tubes reaching the ovary and so are pre-zygotic in action. In contrast, in taxa with late-acting self-incompatibility (LSI), rejection is often post-zygotic, since self-pollen tubes grow to the ovary where fertilization may occur prior to floral abscission. Alternatively, lack of self fruit set could be due to early-acting inbreeding depression (EID). The aim of our study was to investigate mechanisms underlying lack of selfed fruit set in Handroanthus heptaphyllus in order to assess the likelihood of LSI versus EID. Methods We employed four full sib diallels to study the genetic control of LSI in Handroanthus heptaphyllus using a precociously flowering variant. We also used fluorescence microscopy to study the incidence of ovule penetration by pollen tubes in pistils that abscised following pollination or initiated fruits. Key Results All diallels showed reciprocally cross-incompatible full-sibs (RCI), reciprocally cross compatible full-sibs (RCC), and non-reciprocally compatible full-sibs (NRC) in almost equal proportions. There was no significant difference between the incidence of ovule penetrations in abscised pistils following self- and cross-incompatible pollinations, but those in successful cross pollinations were around twofold greater. Conclusions A genetic model postulating a single S locus with four s alleles, one of which, in the maternal parent, is dominant to the other three, will produce RCI, RCC and NRC situations each at 33 %, consistent with our diallel results. We favour this simple genetic control over an early-acting inbreeding depression (EID) explanation since none of our pollinations, successful or unsuccessful, resulted in partial embryo development, as would be expected under a whole genome EID effect.

Parent–offspring conflict and motivational control of brooding in an amphipod (Crustacea)

Models of parent–offspring conflict concerning levels of caregiving centre on conflict resolution by offspring control, compromise or offspring ‘honest signalling’ that parents use to maximize their own fitness. Recent empirical studies on motivational control of parental feeding of offspring are interpreted as supporting the latter model. Here, we examine parental care in an amphipod, Crangonyx pseudogracilis , which directs care to embryos in a brood pouch. Embryo removal and transplantation elucidated causal factors that determine levels of caregiving. In the short-term, females with all embryos removed reduced care activities, but partial embryo removal did not affect caregiving, evidence of ‘unshared’ parental care. In the long-term, females with all embryos removed ceased care. Thus, females have a maternal state that is maintained by stimuli from offspring. Transplantation of early/late stage embryos among females originally carrying early/late stage embryos revealed that stimuli from embryos indicate their age-dependent needs, but only modify caregiving within the constraints of a changing endogenous maternal state. Thus, we demonstrate that mothers and offspring share motivational control of care. However, we highlight the inappropriate use of motivational data in reaching conclusions about the resolution of parent–offspring conflict.

Fertility in Scottish Blackface ewes as influenced by climatic stress

SUMMARYSixty-four Blackface ewes in moderately fat body condition, were divided into two groups at 17 days before a chemically synchronized mating. One group was penned indoors (sheltered group), the other group penned outdoors in a climatically exposed position and subjected to artificial wetting for 6 h daily (exposed group). The ewes were fed a maintenance ration of 1350 g pelleted dried grass/head/day indoors and 1500 g outdoors.The treatment was continued from 17 days premating to 25 ± 3 day post-mating. Immediately after mating 16 ewes from each group were interchanged between the two environments. Matings and returns to service were recorded, and at 25 ± 3 days after first mating the ewes were slaughtered. Counts were made of active corpora lutea and embryos; retarded embryos were distinguished. Fresh weights of the ovaries, pituitary, thyroid and adrenal glands were obtained.Body condition of the ewes within the two environments was maintained. The mean ovulation rates of ewes holding to first service were significantly different (exposed group, 1·52; sheltered group, 1·86). There was no difference between the treatment groups in the number of ewes returning to service, but there was some difference in partial embryo loss, most of which occurred outdoors on or about day 14 or 15 postmating. The results suggest that ovulation rate and possibly early embryo mortality can be influenced by cold stress.