Aphids and Telescoping Generations

Aphid adult and nymphs (Photo credit: humbleseed.com)

If you could imagine an organism that gives birth to offspring that are already pregnant with a third generation, it would look something like a small, green, herbaceous insect. We call them aphids. As one of the world's worst agricultural pests, species of this group of insects exhibit a variety of peculiar reproductive strategies, including this phenomenon of telescoping generations. In many species, all of the overwintered eggs that hatch in the spring result in females, which then reproduce asexually to render generation after generation of genetically-identical female aphids (cyclical parthenogenesis). When autumn arrives, the females give live birth to both male and female offspring, lacking wings and often mouthparts. And upon sexual reproduction of these progeny, the females, rather than giving live birth (vivipary), lay eggs (ovipary) which overwinter and renew the cycle.

Because of the agricultural significance of this insect, scientists have sequenced the genome of one particular species, the Pea Aphid. Read the journal article here.

The Alpine Salamander: Try Beating this Record

The Alpine Salamander (Photo credit: Herpetofauna of Europe)

As the name suggests, this small black salamander lives high in the Alps of central Europe. Living an average of 10 years and measuring 12 centimeters in length, the female typically gives birth to two young after a gestation period of up to three years, depending on its elevation. This is the longest known gestation period of any animal. As you might expect, the young are well developed and quite large, almost half the length of the adult. In the initial stages of embryonic development, one embryo in each uterus is nourished by its own yolk and the yolks of its not-so-fortunate siblings. Once this resource is depleted, the young eat the vitelline mass available in the uterus. And finally, their external gills are used to acquire nutrients from the maternal fluids. Surprisingly, with such a long pregnancy and small number of offspring, these peculiar amphibians are quite common in their current distribution.

Reference: A Compendium of Indispensable Facts (Ben Horslen, 2004)