Parasitic Reproduction

So this week we dive deep down to the bottom of the ocean and look at what I think is one of the most bizarre reproductive behaviours to have evolved, the Anglerfish. 

The Anglerfish is not uncommon and can be found throughout most of the oceans. Although not uncommon, most will have never seen one as they are bathypelagic, occupying ocean habitats below depths of around 300m (Pietsch, 2009). While some species of Anglerfish obtain a "normal" behaviour of reproduction, a suborder of Anglerfish (Ceratioidei) is rather strange. They reproduce by what is referred to as parasitism, where the male will inbed itself to the females body and live off her (Vieira et al., 2013).

The males are dwarfed and will only reach a size of approximately 6-10mm while the females can be more than 60 times that of the male. Males will search the ocean floor looking for a female, once a suitable female is found the male will then latch on to the female by a set of pincher-like denticles (Pietsch, 2005). Once attached the male will then fuse himself from the snout and tip of the lower jaw to tissues of the circulatory system of the female. This allows for the male to remain alive and will be permanently dependent on the female for nutrients (Pietsch, 2005). The benefit to the female is that she obtains a constant supply of sperm for when she is ready to mate. With some families of this species the male can not reach sexual maturity until attached to a female and will obtain undeveloped gonads. 

Parasitic male anglerfish

It is believed that Ceratioidei evolved this way due to the lack of potential partners available. As they live a solitary life and at great depth in the ocean, for both male and female, coming across a mate is hard, especially when it is the exact right time to breed (Piestch, 2005). By the males essentially becoming part of the female body this allows for optimal fertility.

Parasitic attachment of the male to the underside of the female. 

References

Pietsch, T.W.,2005, "Dimorphism, parasitism, and sex revisited: modes of reproduction among deep-sea ceratoid anglerfish (Teleostei: Lophiiformes), Ichthyological research, Vol. 52, pp. 207-236. 

Pietsch, T.W, 2009, "Oceanic Anglerfishes: Extraordinary diversity in the deep sea". University of California press, Los Angeles.

Vieira, S., Biscoito, M., Encarnacao, H., Delgado, J and Pietsch, T. W, 2013, "Sexual parasitism in the deep-sea ceratioid anglerfish centrophryne spinulosa regan and trewavas (Lophiiformes: Centrophrynidae)" Copeia, no. 4, pp. 666-669.