Mating can be a risky behavior for some animal species. The act of mating requires a great deal of energy and can leave some animals vulnerable to predators. For a few species, the mating process is so strenuous that they die shortly after.
Insects That Die After Mating
There are several insects that die soon after mating. This phenomena is known as post-copulatory death. Some examples include:
- Male praying mantises – Females often decapitate and eat the male during mating.
- Male honey bees – The males abdomens and reproductive organs explode after mating due to contractions of the abdomen.
- Male antechinuses – These small marsupial mice have a mating season that is so intense that it destroys their immune system and causes them to die within 2-3 weeks.
- Male dark fishing spiders – Females often cannibalize the male after mating.
- Mayflies – Adult mayflies typically only live for 24 hours and use most of that time for mating before dying.
In most cases, the male dies after mating while the female survives. This makes evolutionary sense in insects that do not provide parental care. Since the male has passed his genes on, his purpose is complete. The female still needs to gestate the eggs and care for the offspring. Dying after copulation allows the male to maximize the number of matings during his short adult life.
Why Do Insect Males Die After Mating?
There are several evolutionary theories as to why insect males die after copulating:
- Removing competition for females – By dying soon after mating, a male eliminates competition and ensures his offspring have access to more female mates in the future.
- Preventing future mating attempts – Death saves energy that would be spent on trying to find and attract new mates.
- Passing on genes quickly – The urgency to mate means males genetically predisposed to quick mating are favored by natural selection.
- Eliminating inferior genes – Weaker males tend to die faster after mating. Only the strongest males survive long enough to mate again.
While post-copulatory death may seem like an extreme evolutionary strategy, it appears to benefit insect species that have short adult lifespans and limited time to reproduce. Males that mate repeatedly produce no more offspring than those mating just once, so an early death carries little cost.
Other Animals That Die After Mating
In addition to various insects, there are some other animals that may die shortly after mating:
- Male salmon – Pacific salmon Migrate upstream to spawn and often die soon after from exhaustion and physiological changes.
- Male giant octopuses – Die a few months after mating from exhaustion. Females survive long enough to care for the eggs.
- Male marsupial mice – As mentioned before, antechinuses experience fatal immune system breakdown triggered by mating season.
- Male black widow spiders – Females often eat the male after mating, although this is variable.
The phenomena of post-copulatory death is less common in vertebrate animals. Male mammals in particular are more likely to continue living after mating so they can have additional opportunities to pass on their genes.
Why Do Other Animals Die After Mating?
There are a few key reasons outside of insects that animals may die after mating:
- Exhaustion – Mating can use up the last reserves of energy. Pacific salmon stop eating once they return to spawn.
- Injury – Males may sustain damage during mating fights with other males or from the female herself.
- Stress – High stress levels during mating can compromise the immune system.
- Trade-off – Investing all effort into mating means neglecting other survival needs.
For male-only deaths, the evolutionary principles are similar to insects. Committing fully to mating may maximize passing on genes even if it leads to an earlier death.
When Females Die After Mating
While less common, there are some instances where the female dies after mating:
- Black widow spiders – Occasionally the female eats the male after mating, but sometimes the male kills and eats the female as well.
- Octopuses – Females usually survive longer to tend the eggs, but many still die within a few months after mating.
- Antechinuses – The intense mating stress can impact female marsupial mice too, leading to death.
- Semelparous animals – Some animals like salmon reproduce only once in a lifetime before dying.
Females that die soon after mating typically do so after ensuring their offspring are cared for. In species with no parental care like octopuses, females may still outlive males by a few months.
Does Mating Really Cause Death?
While mating does appear to lead to an early death for some species, there are a few nuances to consider:
- Correlation vs causation – Just because an animal dies after mating doesn’t mean mating is the direct biological cause of death. Exhaustion from travel, lack of feeding, injury fighting other males, stress, and lack of predator avoidance are also factors.
- Proximate vs ultimate cause – While mating may be the proximate cause of death by exhausting the animal, the ultimate evolutionary cause is passing on genes.
- Variable lifespan – Some animals have very short natural adult lifespans regardless of mating. Mayflies for example only live 24 hours even without mating.
So while mating is linked to early death in some species, it might be more accurate to say that extreme investment in maximal mating effort is associated with rapid senescence and lack of self-preservation behavior.
Examples of Animals That Die After Mating
Here are some specific examples of animals that frequently die shortly after mating:
Praying Mantises
- In most praying mantis species, females eat the male during mating.
- She bites off the head and thorax, providing nourishment to support egg production.
- Male mantises have evolved to continue thrusting after being partially eaten.
- Females get a meal while ensuring fertilization. Males pass on genes at the cost of their life.
Pacific Salmon
- Salmon migrate from the ocean upstream to breeding grounds.
- They cease feeding during migration and use up energy reserves.
- After spawning, females defend the nests as males die from exhaustion.
- Both male and female salmon die within 1-2 weeks of spawning.
Male Antechinuses
- Mating season only lasts 2-3 weeks each year for antechinuses.
- Males mate with as many females as possible during this time.
- The stress and intense mating activates a maladaptive immune response.
- Males can mate so frequently that they get severe ulcers and internal bleeding.
- Most males die before the birthing season ends.
Survival Mechanisms
Some animals have evolved mechanisms to avoid dying immediately after mating:
- Breakaway genitals – Male spiders and other invertebrates may leave parts of their reproductive organs behind to escape hungry females.
- Playing dead – Male spiders like the Steatoda grossa fake their own deaths to avoid cannibalism.
- Castration – Male cephalopods remove their own mating arm, distracting the female long enough to escape.
- Early escape – Some male insects flee the scene immediately after mating.
For vertebrates like mammals, parental care for offspring selected for traits like continued health and survival in males after mating.
Why Don’t More Complex Animals Die After Mating?
There are a few key reasons why death after mating is much less common in vertebrates and mammals in particular:
- Parental care – Many mammalian fathers contribute to raising offspring, so surviving is evolutionarily advantageous.
- Multiple matings – Males can reproduce again, spreading out the energy expenditure.
- Longer gestation – Female mammals need male protection for extended pregnancies.
- Greater complexity – More complex organs and tissues make sudden system failure after mating less likely.
Additionally, the mating period for mammals is normally extended over many weeks or months rather than the very short mating windows seen in insects. This decreases the intensity of sexual selection pressure.
Benefits of Dying After Mating
Despite the obvious individual disadvantage, there are some species-level benefits to animals that die after mating:
- More resources for offspring survival
- Earlier maturation for offspring
- Increased genetic diversity
- Decreased inbreeding
- Potentially faster evolution
Shorter lifespans and high mortality after reproducing help maintain an optimal balance of resources for each generation. Species that die after mating essentially clear ecological space for their offspring.
Disadvantages of Dying After Mating
There are also some disadvantages or costs associated with rapid death after mating:
- Loss of experienced breeders
- Decreased parenting and training of offspring
- Fewer repeat matings
- Greater instability in population size
- Higher predation of juveniles
For species like mammals and birds, parental guidance is extremely beneficial for offspring survival. This selects against rapid death after mating in more complex animals.
Is it All Bad to Die After Mating?
No, dying after mating isn’t entirely negative or suboptimal evolutionary strategy. It depends on the species and context:
- Can maximize gene propagation in short-lived species
- Eliminates mate competition quickly
- Recycles nutrients back into ecosystem
- May increase offspring genetic variability
- Contributes to ecological balance
As long as enough healthy offspring are produced to grow the next generation, dying after mating carries minimal evolutionary disadvantage. It only becomes negative if too few offspring survive due to lack of parental care.
How Can Animals Increase Their Chance of Survival?
If post-mating death is selected against, some adaptations that help animals boost survival after reproduction include:
- Storing extra energy reserves
- Mating efficiently and avoiding injury
- Eating and resting adequately between matings
- Forming monogamous pair bonds
- Sharing in parental care duties
- Delaying senescence processes
For males, maintaining good physical condition after mating helps ensure they can reproduce again in the future. For females, staying healthy allows them to gestate offspring successfully and care for them after birth.
Are There Any Exceptions?
There are always exceptions. Some examples of unusual cases where animals don’t die after or during mating include:
- Male lions defend prides and mate repeatedly
- Male seahorses birth offspring and continue living
- Male wolves assist in provisioning for pups
- Male penguins keep eggs warm and share feeding duties
- Female black widows sometimes spare the males after mating
- A few male praying mantises escape getting eaten
In species where both parents contribute extensive parental care, it is much more evolutionarily advantageous for both males and females to survive mating. Extended biparental care selects against post-copulatory death.
Conclusion
In summary, certain insects and animals die after mating due to the extreme physiological stress and demands of reproduction. This evolutionary strategy maximizes passing on genes for short-lived species. However, it becomes maladaptive when offspring require extensive parental care and training to survive.
For mammals and other complex social creatures, death immediately after mating would be counterproductive. Monogamy and biparental care keep mating investment at sustainable levels. By understanding the costs and benefits of dying after sex, we gain insight into how different reproductive strategies evolve and contribute to the diversity of life histories on Earth.
