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The Intertwining of Nature and Time

The evolution of life is a process that has taken billions of years to produce the species’ we know and love today. This long progression of time has culminated in fascinating species, with their own unique and extreme timelines. The great variation in different animals’ lifespans and gestation periods, as well as the internal clocks that species possess are all fascinating examples of the relationship between nature and time.

When thinking about the longest living organism in history, the clam may not be the first animal to pop up in one’s mind. However, a species of clam named Arctica islandica has taken first place for the longest lived species (1). In a study done to determine the age of these clams, one clam that was collected was estimated to be 407 years old (1). A. islandica has annual growth rings, and this ancient specimen possessed 405 (1). However, during the first and last years of its life, this clam species does not produce annual rings, thus increasing the lifespan estimate from 405 years to 407 years (1). 

Elephants are another long-lived species, reaching ages of over 80 years old (2), but they are no match against the ancient A. islandica. However, elephants are number one for a different record: longest gestation period of any animal. These giant mammals are pregnant for up to 22 months (3), more than double the gestation period of a human. Elephants are K-strategists, which means that they have long gestation periods and take a significant amount of time to rear their young. Another characterization of K-strategists is producing fewer offspring with relatively long intervals between each pregnancy. In one study examining African elephants (Loxodonta africana), it was determined that there is an average birth interval of 4.5 years (2). 

Looking at the other side of the reproductive spectrum, we can see an example of a mammal with an extremely short birth interval: eastern cottontail rabbits (Sylvilagus floridanus). Female eastern cottontails are able to get pregnant within the first 30 minutes after giving birth and have a gestation period of 26 – 28 days (4). In one study done in Oregon, it was estimated that one population of eastern cottontails had a maximum of eight litters in a 218 day long breeding period (5), which gives an average gestation period of 27 days. 

Illustrations by Isabel Alcantara

Time is an important part of the hatching process for species of birds that practice asynchronous hatching, which is when a single brood hatches at different times. The babies that hatch first are typically larger than the ones that hatch later, and have a higher position in the nest hierarchy (6). One hypothesis for why these birds practice this type of hatching is that during times of food scarcity, the overall survival rate of the brood is better when the oldest are prioritized and receive more food than the youngest, rather than having all of the babies fed equal amounts (6).

Perception of the time of day can be immensely important in many animals for various reasons, one of which is for migration. Certain populations of monarch butterflies (Danaus plexippus) have been seen to undergo an annual migration from America to the Transverse Neovolcanic Belt of central Mexico, going as far as 3600 km in a span of 75 days (7). These butterflies are able to make this dramatic migration by utilizing the sun as a compass (8). They do this by changing their body orientation based on the time of day and position of the sun (8). Using this “compass” allows monarch butterflies to reach their destination in those forested mountains, where they overwinter. 

Every species has a unique relationship with time, which is seen in those animals’ respective lifespans, gestation periods, birth intervals, brood development, and internal clocks. Time touches every aspect of life, from major life periods such as mating seasons and migrations, to daily functions such as the time of day to hunt and rest. 

Article written by Sammi Duven, Colorado Parks & Wildlife

References:

1. Wanamaker, A. D., Jr., Heinemeier, J., Scourse, J. D., Richardson, C. A., Butler, P. G., Eiríksson, J., & Knudsen, K. L. (2008). Very long-lived mollusks confirm 17th century AD tephra-based radiocarbon reservoir ages for North Atlantic shelf waters. Radiocarbon, 50(3), 399-412. https://doi.org/10.1017/S0033822200053510

2. Moss, C. J. (2001). The demography of an African elephant (Loxodonta africana) population in Amboseli, Kenya. Journal of Zoology, 255(2), 145-156. https://doi.org/10.1017/S0952836901001212

3. Oerke, A. K., Heistermann, & M. A., Hodges, K. (2006). Duration of pregnancy and its relation to sex of calf and age of cow in the European population of Asian and African elephants. In: Proceedings of the international elephant conservation research symposium. 125-131. 

4. Marsden, H., & Conaway, C. H. (1963). Behavior and the reproductive cycle in the cottontail. The Journal of Wildlife Management, 27(2), 161-170. https://doi.org/10.2307/3798393

5. Trethewey, D. E. C., & Verts, B. J. (1971). Reproduction in eastern cottontail rabbits in western Oregon. The American Midland Naturalist, 86(2), 463-476.  https://doi.org/10.2307/2423637

6. Lack, D. (1969). The evolution of reproductive rates: ecological adaptations for breeding in birds. Science, 163(3872), 1185-1187. https://doi.org/10.1126/science.163.3872.1185

7. Brower, L. P. (1996). Monarch butterfly orientation: missing pieces of a magnificent puzzle. Journal of Experimental Biology, 199(1), 93-103. https://doi.org/10.1242/jeb.199.1.93

8. Perez, S. M., Taylor, O. R., & Jander, R. (1997). A sun compass in monarch butterflies. Nature, 387, 29. https://doi.org/10.1038/387029a0

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