The consequences of alternative parental care tactics in free-ranging pythons in tropical Australia

Authors


Correspondence author. E-mail: zrs@dal.ca

Summary

1.Life-history theory attributes the evolution of parental care to the benefits to offspring viability outweighing any costs to parental viability. However, the consequences of parental care tactics to parent(s) and the developmental environment have seldom been measured under field conditions.

2.Laboratory research on pythons shows that maternal nest-site selection and egg brooding benefit embryos, but prolonged nest attendance may impose fitness costs to free-ranging females. A population of water pythons (Liasis fuscus) in tropical Australia provides an excellent opportunity to examine this parent–offspring trade-off because females exhibit parental care polymorphism wherein some individuals brood their eggs only briefly (<10 days) post-oviposition (‘short brooders’) while others remain with their eggs throughout the incubation period (>50 days; ‘long brooders’).

3.We used radiotelemetry, temperature and humidity data loggers, ultrasonography, haematological techniques, and habitat analyses to examine the correlates and consequences of maternal nesting decisions in 14 free-ranging female pythons over the 4-month reproductive season.

4.Nest-site selection and maternal attendance enhanced thermal and hydric regimes within the nest. Egg production by reproducing female pythons resulted in high energetic costs (loss of 60% of maternal body mass) and increased parasite load. However, the estimated mass loss because of brooding was (i) low (<5%), (ii) inversely related to fecundity (females that produced relatively large clutches tended to select lower temperatures and thus lost less mass during brooding) and (iii) surprisingly unrelated to brooding duration. Phenotypic traits of short and long brooders were similar, but long brooders had higher haemoparasite burdens prior to oviposition. Clutches of long brooders were laid in more open sites (less canopy cover) and experienced warmer and more humid conditions than did those of short brooders.

5.Together with previous research, we suggest several explanations for the maintenance of maternal care polymorphism within this population, such as a trade-off between offspring number and quality (long brooders may produce fewer clutches during their lifespan but enhance offspring quality). Our study provides detailed measurements of the correlates and consequences of parental care in a free-ranging reptile, and it clarifies the trade-offs mediated by taxonomically widespread maternal decisions (e.g. nest- or oviposition-site selection and nest attendance).

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