My readers know that there are two biological subjects near and dear to me, and common in all species... eating and sex (er, reproduction)! Like my icons Edward "Doc" Ricketts and John Steinbeck, I believe these are the two key activities of all life on Earth. Why? Because the ultimate purpose of life is to reproduce... to pass one's genes on to the next generation. Of course humans infuse life with greater meaning, often of a religious nature. Since that subject is usually too controversial to appear in my columns, I'll stick to the less controversial topic of sex! My sex life is nothing to write about, so I want to focus on some truly strange reproductive lifestyles in the marine world. They make anything we humans have dreamed up (even in Hollywood) pale by comparison!
By now my readers are familiar with our own "Hollywood fish" of the kelp forests, the sex changing sheephead. All sheephead begin life as females and many will switch genders, becoming males as they get older. Other wrasses in our area like the rock wrasse may also start off as females and turn into males, a process known as protogyny ("first female"). Some species in other families begin life as males, then switch to being female (known as protandry). If you ask me, this makes more sense (at least for my fishy friends). Males produce sperm, which are much smaller than eggs. A young, and therefore smaller, fish could produce far more individual sperm cells than eggs. An older, and larger, fish could produce far more eggs than a small one.
If passing on one's genes is the ultimate biological purpose of life, the ability to change sex may confer certain "advantages" on an animal. Some biologists say it doubles the fish's chances of mating, but I don't see it that way for species which change sex as they age. While female, they can mate only with males... and when they turn male, they can only mate with females. Where sex change does seem to be a real advantage for fishes that live their entire lives in one area is in ensuring there will be both females and males available to mate with. If a "big bad fisherman" (like those on the Newport Beach based charter fishing boat "Freelance" that seems to like hovering just outside the marine reserve at the Dive Park) catches the dominant male sheephead in an area, there may be no available males left to mate with the many females. The ability of a female to become a male ensures that mates will be available even if the dominant ones are caught.
One wrasse that I've encountered frequently in the Caribbean and off Florida is the bluehead wrasse. The younger yellow females of this species are abundant and tend to swarm across the reef. They are frequently the most prolific of the cleaner species on a reef. The beautiful blue and green dominant males are much fewer in number. They mate with their "harem" of females. Should the male be eaten by a predator, a female can change sex and replace it. Amazingly, this change may require only minutes to complete. It doesn't even require a costly sex change operation.
Such sex changing fishes often have gonads (reproductive structures) that have both male (testis, singular of testes) and female (ovary) parts. A region in the fish's brain known as the hypothalmus may respond to a "trigger" within the environment such as the absence of a dominant male. It then causes the pituitary gland to start producing male instead of female hormones. The ovaries go into production and the testis ceases to produce sperm. Other species take longer to effect this gender bending transition.
Fish that begin as one sex and change into the other are known as "sequential hermaphrodites." They are either male or female, but not really both. Fish which can function as either male or female at the same time are known as "simultaneous hermaphrodites" because they are of both genders. Imagine the confusion that must cause in their sexual identity. However being in this state confers a tremendous advantage on these species, just as it does for the beautiful nudibranchs which may also have both sex organs functioning at the same time. No matter "who" you meet while cruising the reef, it will be someone you can mate with! In terms of passing on your genes, that is a real plus. However, in terms of selecting the appropriate restroom, it could be very difficult!
One fish that I recently discovered was a simultaneous hermaphrodite, both male and female at the same time, is the tobacco fish. I first encountered this species in Belize, and saw it again recently in Florida. The first time it was just a solitary individual, but the second time there was a pair together on the reef. At the time I didn't realize I was watching a species which had not just one means of mating (male and female), but two... first male with second female, or first female with second male.
Another group of simultaneous hermaphrodites I've encountered on coral reefs are the small basses known as hamlets. Their mating behavior is truly interesting (at least to a film maker who focuses on underwater "porn" like myself). Hamlets display what is known as egg trading. Starting shortly before sunset each evening (yes, each and every evening!), hamlets start acting as if they are being dominated by their hormones... and they are. The hamlets leave their territories and seek out their regular mates which may be as far away as 100 yards (sigh, if only mine were that close).
The hamlets chase around the bottom for about an hour until one of them takes on the female's role as the aggressor (what a great concept), snout up and fins flared out. The male, with its colors seemingly bleached, awaits nose down until she clasps him and they spawn for a whole three seconds (such staying power). This behavior is repeated, with the two fish reversing their sexual roles in the coupling. This may go on for up to 10 encounters. Afterwards, the fish retire individually for a much deserved rest before the next evening's tryst.
As for me, I'm quite happy knowing that my gender is fixed. It makes it far easier for me to identify potential mates, especially as my eyesight declines. In large cities where the androgynous look has been adopted, I could easily get a bit confused without my bifocals and biological expertise!. Of course I've already passed my genes on to the next generation (your turn, Kevin... but I'm not anxious to be a grandfather yet so take your time). I guess that means any "mating" I get an opportunity to indulge in will only be practice for my next life. Of course the more practice I get in this life, the better I'll be in my next incarnation!
© 2005 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 49, 10:00 AM and 5:00 PM weekdays.
Swarm of young female blueheaded wrasses, closeup of a
dominant male bluehead wrasse;
tobacco fish and indigo hamlet
This document maintained by
Dr. Bill Bushing.
Material and images © 2005 Star Thrower Educational Multimedia