Rapid population sex-ratio changes in the moss Ceratodon purpureus

PREMISE OF THE STUDY

Sex-ratio variation occurs widely in dioecious plants, but the mechanisms of population sex-ratio bias are poorly understood. In bryophytes, sex ratios are often female biased, and little information is available about how and when bias forms.

METHODS

To test whether population sex-ratio variation can emerge during the gametophytic phase and is not purely a product of spore sex ratios, we created artificial populations of the moss Ceratodon purpureus, with male- and female-biased sex ratios, and placed half under a stress treatment. We hypothesized that male-majority populations would become female-biased and that stress would increase this transition. After 18 mo, when sporophytes were initially forming, we used sex-specific molecular markers to determine population sex ratios.

KEY RESULTS

Female-majority populations did not differ significantly from their original bias, whereas male-majority populations became significantly more female biased. The plants had only just produced their first spores, so these sex-ratio changes occurred during the gametophytic generation, as a result of sex-specific growth or survival. Sporophytes occurred only in populations with female-biased final sex ratios, which suggests that females in male-majority populations may have invested energy in ramets rather than in sporophyte production. The stress treatment was mild and had no effect on sex ratio.

CONCLUSIONS

Our results suggest that female bias can be generated during the gametophytic generation, before plants reach sexual maturity. These results, combined with those of previous work, suggest that both the gametophytic and the sporophytic stages drive population sex ratios in C. purpureus, thus indicating that multiple mechanisms operate to create biased population sex ratios.

Insulin-like growth factor signaling regulates developmental trajectory associated with diapause in embryos of the annual killifish Austrofundulus limnaeus

Annual killifishes exhibit a number of unique life history characters including the occurrence of embryonic diapause, unique cell movements associated with dispersion and subsequent reaggregation of the embryonic blastomeres, and a short post-embryonic life span. Insulin-like growth factor (IGF) signaling is known to play a role in the regulation of metabolic dormancy in a number of animals but has not been explored in annual killifishes. The abundance of IGF proteins during development and the developmental effects of blocking IGF signaling by pharmacological inhibition of the insulin-like growth factor I receptor (IGF1R) were explored in embryos of the annual killifish Austrofundulus limnaeus Blocking of IGF signaling in embryos that would normally escape entrance into diapause resulted in a phenotype that was remarkably similar to that of embryos entering diapause. IGF-I protein abundance spikes during early development in embryos that will not enter diapause. In contrast, IGF-I levels remain low during early development in embryos that will enter diapause II. IGF-II protein is packaged at higher levels in escape-bound embryos compared with diapause-bound embryos. However, IGF-II levels quickly decrease and remain low during early development and only increase substantially during late development in both developmental trajectories. Developmental patterns of IGF-I and IGF-II protein abundance under conditions that would either induce or bypass entrance into diapause are consistent with a role for IGF signaling in the regulation of developmental trajectory and entrance into diapause in this species. We propose that IGF signaling may be a unifying regulatory pathway that explains the larger suite of characters that are associated with the complex life history of annual killifishes.

Embryonic development of the annual killifish Austrofundulus limnaeus: An emerging model for ecological and evolutionary developmental biology research and instruction

BACKGROUND

Austrofundulus limnaeus is an annual killifish from the Maracaibo basin of Venezuela. Annual killifishes are unique among vertebrates in their ability to enter into a state of dormancy at up to three distinct developmental stages termed diapause I, II, and III. These embryos are tolerant of a wide variety of environmental stresses and develop relatively slowly compared with nonannual fishes.

RESULTS

These traits make them an excellent model for research on interactions between the genome and the environment during development, and an excellent choice for developmental biology laboratories. Furthermore, A. limnaeus is relatively easy to maintain in a laboratory setting and has a high fecundity, making it an excellent candidate as an emerging model for studies of development, and for defining the limits of developmental buffering in vertebrates.

CONCLUSIONS

This study reports for the first time on the detailed development of A. limnaeus and provides a photographic and illustrated atlas of embryos on the two developmental trajectories possible in this species. Developmental Dynamics 246:779-801, 2017. © 2017 The Authors Developmental Dynamics published by Wiley Periodicals, Inc. on behalf of American Association of Anatomists.