In part 1 we came upon the topic that in the animal kingdom, males have a hard time trying to produce offsprings due to the different level of investment made by males and females. Therefore females are more limited in reproductive potential therefore they have the privilege to pick which male to mate with, resulting in competition between males for mate. But securing a mate is one thing, the journey for males do not stop here. A female can always guarantee that their offspring will contain half of her genes as it is her that gives birth, yet male paternity is shrouded by a constant uncertainty.
Extra-pair copulation, termed polyandry, is not uncommon in the animal world, For many passerine bird species, any given clutch may contain eggs fathered by 2 or more males. Mating with multiple males can provide many benefits for females such as extra direct/indirect benefit and replenishment of sperm stock, however such unfaithful behaviour has no benefit for males therefore it is unsurprising that a variety of anti-cuckoldry behaviour has evolved.
To gain that extra assurance many males decided to make some extra investment in offspring reproduction. One way is mate/egg guarding, preventing access of other males. Such behaviour has been observed across a wide variety of animals. Male water striders sit on the back of its mate for several days before mating, in order to deny access too the female. Male baboons often watch over females it has mated with for a period of time after copulation.
Guarding a mate that is mobile pose a high energy cost in which the male has less time to feed itself, guarding immobile eggs is a less taxing alternative. Male giant water bugs carry eggs of their partner on its back with him, to ensure that he’s not guarding another male’s offspring, it will mate with the female repetitively, up to 40 times, before allowing the eggs on his back. Pipefish and seahorses do not resort to such a “brutal” method, males have a adapted brood pouch where the female deposit the egg into after external fertilization. Males effectively act as incubators and gives birth to live young. This method assures that all offspring hatched are those of the male’s.
To enforce the passing on of their genes, some males have adapted quite extreme behaviours. Male lions, after successfully taking over a pride from its original male leader, will proceed to kill all offsprings of the previous pride holder. This behaviour is also witness in many primate species. This act of infanticide has 2 purpose, it prevent consumption of valuable resource by cubs that are not genetically related to the male, secondly it brings the females of the harem into heat.
Sometimes you may not be the first one to get lucky with the lady, if that is the case then the male risk losing some of the female’s reproductive potential to others. Some male insects deploy a sperm displacement strategy to remove the sperm of previous rivals from the female’s spermatheca. Male dragonfly and damselfly species evolved specially shaped penises with barbs specific to the shape of the female’s spermatheca, in order to plough out the sperm of pervious males and increase fertilization success.
In a most extreme example, “rape” is adopted by males in order to establish its own sperm final precedence in the female. In a behaviour termed traumatic insemination, male bedbugs forcifully attach to females and wield its barb-like penis like a sword to stab into the female’s belly, and then ejalucate directly into the female’s haemolymph (equivalent of blood). The injected sperm is stored in an adapted female gland and released during the female’s next bloodmeal when she will be able to produce a batch of eggs. In addition, larger males will also rape smaller males to inject their sperm into the victim’s sperm duct, therefore when the victim rapes a female he will be using a portion of his rapist’s sperms. This really is an example where male will do virtually anything to assure 100% guarantee of their paternity.
Despite that males are naturally at a disadvantage to complete the utmost goal of one’s life cycle, evolution has provided unique strategies to combat such scenarios. On the quest to fatherhood is where many wonders of the animal world came to fruitation.