Title. Evolution of maternal investment strategies for the Strawberry Poison-Dart Frog, Dendrobates pumilio, based on environmental risk factors

Transcription

1 Title Evolution of maternal investment strategies for the Strawberry Poison-Dart Frog, Dendrobates pumilio, based on environmental risk factors Author Richard Pashkow:

2 Abstract The strawberry poison dart frog (D. pumilio) is a small amphibian that lives in low land tropical forests in places such as Madagascar and Puerto Rico. Females can reproduce multiple times throughout the entire year, yet only ovulate during favorable (moist/wet) conditions, and can lay 4 to 6 eggs a clutch. These frogs are one of, if not the best amphibian parents in the animal kingdom. They will actively take care of their offspring from the time of laying the eggs all the way up until the time of metamorphosis of the young. We conclude that starvation is a much greater threat to offspring survival than predation.

3 Introduction The strawberry poison dart frog (D. pumilio) is best known for its bright colors. These displays of vibrant fashion tell predatory animals to stay away, and yet they are also used to attract insects, and potential mates. These frogs mate any time of the year, but most of the mating occurs most likely occurs during the wetter seasons where frogs can number up to 400 individuals per acre. These frogs will find a small pool of water among the leaf litter to lay their clutch of 4-6 eggs. Both parents will come back to the eggs every day. The male will transport water via the cloaca to keep the eggs from drying out. After hatching the female will carry the tadpoles one by one to their own Bromeliad sanctuary. She will then return every day to each offspring and will deposit up to 5 unfertilized for each young for them to eat because the small bits of algae and insects found in the Bromeliad are not enough to sustain them. Method Offspring number and relative offspring body-size were plotted on the inner x and y axes. The outer x and y axes are qualitative probabilities of predation or starvation. The relative body size of offspring at independence and thus the probability of starvation was estimated as S = m / M where S = expected probability of offspring mortality based on cycles of food scarcity; M = mass of mother at the time of offspring independence; m x = mass per offspring at the time of its independence. The expected probability of offspring mortality by predation was estimated as P = 1 (2/N) where P = expected probability of predation; 2 = expected lifetime fitness per mother; N = the number of offspring produced by a mother per clutch or lifetime. The expected probability of offspring mortality in multiple-risk environments is estimated as PS.

4 Results Figure 1: The maternal investment strategy of the strawberry poison dart frog. P: Predation environments favor investments in offspring quantity rather than quality. S: Seasonal environments that cycle between abundance and scarcity favor investments in offspring quality rather than quantity. R: Multi-risk environments with high predation and periods of scarcity select for a few high-quality offspring and many-low quality offspring. U: Utopian environments favor few, low quality offspring. Discussion The strawberry poison dart frog may be a small individual but is enormous when it comes to parental care. Studies show that a male will dedicate up to 5 hours of parental care while the

5 female can dedicate up to 8 days of parental care. This figure is staggering when compared to other amphibians. This level of parental care is usually only found in mammals. The offspring have very little to no threat as tadpoles because of where the female puts them to mature (metamorphosis). As adults they have little to fear (a few species of snakes) because they become naturally poisonous due to some molecules found in their natural prey. One of the things that these frogs need to fear is loss of their habitat. Humans/Deforestation is one main reason why we are losing the incredible organisms that this planet has given us. Based on the calculations done, one could reason that the maternal investment strategy of the strawberry poison dart frog, which is investing more in offspring quality than quantity, has likely been shaped by environments with a low probability of predation and a high probability of starvation.

6 References Chang, J. L. (2008). Sexual dimorphism of the second-to-fourth digit length ratio (2D : 4D) in the strawberry poison dart frog (Oophaga pumilio) in Costa Rica. Journal of Herpetology, 42(2), doi: Pröhl, H., & Hödl, W. (1999). Parental investment, potential reproductive rates, and mating system in the strawberry dart-poison frog, Dendrobates pumilio. Behavioral Ecology and Sociobiology, 46(4), Pröhl, H., & Berke, O. (2001). Spatial distributions of male and female strawberry poison frogs and their relation to female reproductive resources. Oecologia, 129(4), doi: /s Pröhl, H. (2002). Population differences in female resource abundance, adult sex ratio, and male mating success in Dendrobates pumilio. Behavioral Ecology, 13(2), doi: /beheco/ Summers, K.., Bermingham, E., Weigt, L., McCafferty, S., & Dahistrom, L. (1997). Phenotypic and genetic divergence in three species of dart-poison frogs with contrasting parental behavior. journal of HEREDITY, 88(1), 8-13.