It’s tough being a dude part 2

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.

baboon

yellow baboon

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.

seahorse

pregnant male seahorse. Photograph: Jaro Nemcock

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.

 

 

It’s tough being a dude part 1

To pass on ones gene is an imperative goal for any animal, unfortunately if you are a male, the odds are stacked against you compared to a female. This is because male invest a lot less than females in reproduction, by producing sperm. Compared to the female’s egg, sperm cells are light, nimble and a lot cheaper to produce, allowing males can mate many more times than females. As a result, females tend to be picky over their hubby choices, and it is up to the poor males to win over the heart of the lady.

The first step

In the ever-going sexual struggle, a male must first gain access to a female, and knowing that females are limited in reproductive potential, you can expect a lot of competitors. In the animal kingdom a male’s strategy to out-compete each other can be roughly divided into 2 types.

Brute force

For this style of tactic, males will actively engage with one another in some form of combat, the result is obvious, winner of the contest gets the lady and the loser back off with nothing. Many males have evolved weapons to better arm themselves for such engagements, e.g. stag antlers, horns of stag beetles etc. This kind of tactic often yield massive rewards for the victor, in which the winner gains mating rights to a large number of females in the proximity. However, no pain, no gain. The risk of injury for such tactics are great, therefore many males evolved ways to judge each other’s fighting ability, before they actually scrap it out, red deer stags conduct parallel walks with one another to size each other up. Usually the weaker individual will back off before proper fighting to avoid injuries.

whitetail deer. Photograph: Brian Stansberry

whitetail deer. Photograph: Brian Stansberry

 

 Seduction

For the other tactic, instead of active combat, males compete by attempting to excite or charm females through countless strategies, such as elaborate visual displays or the presentation of a “gift”, while females adopt a more active role and select the preferred partner for themselves. Many theories has been proposed to offer explanation to female choices in such scenarios. The wooing methods may be adapted to exploit a pre-existing sensory bias within the females, it has been discovered that the female tungara frog ancestors had a natural preference for “chucks” in male’s songs, this song preference drove the speciation of the tungara frog.Unfortunately, “chucks” also attract bats which feed on the frogs therefore males only sing “chucks” when in groups.

For some females, a particular male trait may be indication to some kind of genetic advantage that can be passed onto its offspring, which drives the female’s decision making. Such advantages may be a direct fitness advantage such as parasite resistance, or indirect mating advantage in offspring by inheriting the father’s high attractiveness.

Indian peacock display. Photography: Dinesh Kannambadi

Indian peacock display. Photography: Dinesh Kannambadi

Sometimes females may require direct benefit to maximise reproductive success and provision of a food item may be required to win the heart of the lady. Many male insects are known mates with benefits. Male hanging scorpion flies present a food item to females prior mating, while male bush crickets present a portion of its own spermatophore to females as nourishment to persuade it to mate.

 

Due to the female’s disproportionate investment in reproduction, it earned the right to pick its partner for themselves, while males have to spend resource and effort to earn a mate. However the arduous journey for males do not end here, I will talk about it in the next blog how competition doesn’t end for us poor guys even after mating.

Killer whales: wolves of the sea

In this post I want to talk about one of my favourite animals ever since my childhood. A star of the film series Free Willy and Attenborough’s trials of life documentary (it was heaven), yes I am talking about the awesome killer whale!

killer whale, also known as orca, is a toothed whale that can be found in all of the world’s oceans, ranging from the polar regions to the tropical seas. As a species, the whales have a diverse diet which range from fish to marine mammals, and even large whales, however their diet varies across geographic areas. Living in pods, it is a highly intelligent animal that show evidence of culture in individual groups.  The whale’s sophisticated behaviours have been observed to vary among pods, and are passed across generations. One of their particular feature that made me love them so much is their unique adaptations in hunting behaviour across the globe, as demonstrated in numerous documentaries I have watched on the animal, which I am delighted to share with you in this post. orca

At Peninsula Valdes, Off the coast of Patagonia in South America, South American sea lions come to shore annually to breed and give birth. The nursery beach offer a feeding bonanza for a particular pod of killer whales that return annually. Normally you would think that as long as the sea lions remain onshore they would be safe, however this group of killer whales has learned to deliberately beach themselves, the only whale known to do this, by utilizing known water channels. As a result we see black submarines charge ashore and drag back any unfortunate sea lion that was too close. After it is beached, the whale thrashes its body to wriggle back into the wave. This technique requires a long period of learning for youngsters, and is restricted to whales of that region.

In Antarctica, it is a different story. Imagine if you’re a hungry orca wanting a penguin for lunch, and there are a flock of marine poultry on the ice, however they won’t enter the water as they know you are here, what do you do? Time to meet the Antarctic orca’s “wave wash” technique! To “persuade” their prey to enter water, the orca gather comrades and swim towards the ice floe from a distance away. Due to the size of the animal, an orca squad swimming at full speed generates a lot of water, just before reaching the ice, the squad makes a turn, creating a huge wall of water which pushes lunch into the sea. This technique is also applied to seals, perfectly captured in a footage from the BBC’s Frozen Planet.

In terms of hunting, the orcas are perhaps most famous for their ability to kill large whales, the only natural predator of many baleen whale species, even the blue whale, the largest animal that ever lived. Whilst hunting whales, orcas prefer to pick the weak or young individuals, after continuous chasing which wears the animal out, the orcas surround the animal and prevent it from surfacing, drowning it. For more healthy individuals, a wound-and-withdraw tactic is adopted, as observed in sperm whale hunting by orcas.

You might think sharks are the king of the sea, and nobody messes with them, well if so then you are mistaken. In the ocean it is the orcas that rule supreme. Orcas has been witnessed to kill sharks by exploiting the fish’s instinct to enter tonic immobility. Tonic immobility is an instinctive reflex which causes the animal to enter a state of paralysis, and can be induced in many shark species by inverting the animal. In 1997 an eyewitness case reported an orca charging a great white from beneath, flipping the shark and held it in its mouth for 15 minutess until the shark suffocated. This was the first observation of a great white predation by a non-human species, truly demonstrating that orcas is the ocean’s top predator.

An orca holding a great white upside-down in its mouth. Source: Blackfish Sounder, issue 6

An orca holding a great white upside-down in its mouth. Source: Blackfish Sounder, issue 6

 

The remarkable hunting capability of killer whales is truly astonishing, it is capable of preying on virtually any sizeable animal in the ocean. With a diverse range of prey, comes a diverse range of hunting techniques, perfected over time. A more in-depth coverage of the killer whale’s prey range and tactics can be found here. This magnificent animal is truly a perfect mix between brain and brawn.

 

Defensive copycats

Background information

For all animals, the most basal and fundamental desire is to survive and pass on its genes through its generation, however in the cruel natural world many animals face the danger of predation. As a result numerous strategies were evolved in the animal kingdom to reduce predation, one such strategy is mimicry. Mimicry is the similarity of one species to another in which the mimics, develop characteristics similar to another species, termed the model. This process of imitation, when used in defence, aims to reduce predator-prey encounters by deceiving enemies into treating the mimic as something else. For this article I shall talk about some intriguing examples of defensive mimicry in the animal kingdom.

Batesian mimicry

Many species, through evolution, developed traits making themselves unprofitable for consumption by predators, e.g. they may be toxic or has a bad taste. This predator-deterring trait is often accompanied by some form of signal, such as unique skin patterns.  Such signals offer potential for mimicry by species that are less able to deter predators. In Batesian mimicry, a more edible species (mimic) imitates the signals released by more unprofitable species (model), this sheep in wolf’s clothing disguise aims to confuse predators to recognize the harmless mimic as more unprofitable species. The phenomenon was first described by the British naturalist Henry Bates.

A classic example of this phenomenon is the imitation of the poisonous coral snake’s patterns by the non-toxic milk snake. In California there is a well-known mnemonic to help distinguish the 2 species.

“Red to yellow, kill a fellow. Red to black, venom lack.”

Left: milk snake, right: coral snake. Image courtesy of the West Texas Herpetological society.

Left: milk snake, right: coral snake. Image courtesy of the West Texas Herpetological society.

Mullerian mimicry

This form of mimicry describes the case when multiple species share similar warning signals, and all species involved contain anti-predator traits. Normally we would think if both species have anti-predator attributes, what is the point in mimicking each other? The German naturalist Fritz Muller put forward the explanation that if a common predator were to confuse one species with another, since both possess similar signals, then both species will benefit as the predator will stay away from the shared signal. Mullerian mimicry is unique because both the model and mimic benefit in this case.

The Heliconius butterflies from the western hemisphere is a classic example of a Mullerian complex. All members of the species have a bad taste for predators.

heliconus

Heliconius butterflies forms a well-known Mullerian complex.

 

Gilbertian mimicry

This rare form of mimicry involve plants belonging to the passiflora genus, and species of Heliconius butterfly larvae. The leaves of the plant are toxic which deter most herbivores, however Heliconius larvae can break down such toxins. As a result passiflora plants developed outgrowths that resemble Heliconius eggs near the point of hatching. The reason they do this is because Heliconius butterflies prefer to lay eggs away from already existing ones, in order to minimize intraspecific competition after the eggs hatch. In addition, such egg dummies provide nectaries which attract predators of the caterpillars such as wasps, offering extra protection.

A monarch butterfly larvae feeding. Photograph: Derek Ramsey

A monarch butterfly larvae feeding. Photograph: Derek Ramsey

Protective automimmicry

Automimmicry is when both the mimic and the model belong to the same species. This has interesting applications in defence.

For many predators, the head of the prey is the first target choice of attack due to its high vulnerability. Some species exploit this basal instinct via automimmicry. The Four-Eye Butterflyfish conceal its real eyes with a black stripe and has a false eye spot near its tail, giving the impression that the head is at the tail end of the body.

The Four Eye Butterflyfish. Source: en.wikipedia

The Four Eye Butterflyfish. Source: en.wikipedia

Many predators require movement from the prey as a stimulus to hunt it down and kill. Some species actively play dead, hinging on the predator becoming unresponsive to a “dead” prey. This behaviour of feigning dead is termed thanatosis in biology, and is practiced by some well-known species, an example is the hog-nosed snake. When threatened, the reptile rolls onto its back and releases a foul-smelling fluid, giving strong impression of a rotting corpse. This is demonstrated in the video below, I know some people may criticize the videomaker for being rough with the animal, but he is only doing it to trigger the snake’s defence mechanism. Afterall we can’t expect an actual predator to be gentle with this remarkable reptile.