Butterfly Kisses Lead to Decrease in Mating?

Contributed to by Caitlin Brennan, Paige Hogen, Eliot Littlefield, Lauren Taylor and Kathryn Trinka

Many species produce pheromones to communicate with other members of their species. Most people think of pheromones as chemicals used to attract potential mates. However, studies have shown that insects such as butterflies, moths, and other insects produce pheromones with the opposite effect following mating (Greenfield 1981).

How could a mechanism that reduces mating have evolved? One hypothesis describes how these pheromones could have been favored due to male competition. Female Heliconius butterflies naturally release these pheromones when they are not ready to mate, but males also transfer pheromones to females during mating. This causes the female to involuntarily release the pheromone, repelling other males when she would otherwise be receptive to mating (Estrada et al. 2011).

Similar to butterfly pheromones, if a guy with a lot of cologne hugs a girl, she will smell like his cologne for the rest of the day. From that point on, other guys throughout the day will be off put by her smell.

Similar to butterfly pheromones, if a guy with a lot of cologne hugs a girl, she will smell like his cologne for the rest of the day. From that point on, other guys throughout the day will be off put by her smell.

When a male green-veined white butterfly begins to court a female, she initially responds with a refusal gesture. If she is carrying repellent pheromones from another male, this posture causes her to release these pheromones. The courting male perceives her rejection more strongly than he would without the pheromones, and is less likely to continue courting her. By preventing other males from mating with the female, the first male gains a fitness advantage by ensuring that the female’s offspring are his (Andersson 2004).

Interestingly, individuals in the butterfly species Heliconius sara generally mate with only one partner, in the same way that some people eat lunch with only one person; while individuals in the species Heliconius cydno mate with many partners, just as some people might eat lunch with a huge group of people (Estrada et al. 2011). Males of the species H. sara generally have weaker pheromones because in their butterfly culture of having one single mate, there is not as much competition between males to find a mate. In contrast, males of the species H. cydno have strong pheromones, because in their butterfly culture, competition deterring other males from mating with “his girl” dramatically increases the odds that that female will produce his offspring and not somebody else’s.

For Further Reading:

Catalina Estrada, Stefan Schulz, Selma Yildizhan and Lawrence E. Gilbert. 2011. Sexual Selection Drives the Evolution of Antiaphrodisiac Pheromones in Butterflies. Evolution. Vol. 65. No. 10: pp. 2843-2854.

Johan Andersson, Anna-Karin Borg-Karlson and Christer Wiklund. 2004. Sexual Conflict and Anti-Aphrodisiac Titre in a Polyandrous Butterfly: Male Ejaculate Tailoring and Absence of Female Control. Proceedings: Biological Sciences. Vol. 271, No. 1550: pp. 1765-1770.

Ally R. Harari, Tirtza Zahavi and Denis Thiéry. 2011. Fitness Cost of Pheromone Production in Signaling Female Moths. Evolution. Vol. 65, No. 6: pp. 1572-1582

Michael D. Greenfield. Moth Sex Pheromones: An Evolutionary Perspective. 1981. The Florida Entomologist. Vol. 64, No. 1: pp. 4-17

Johan Andersson, Anna-Karin Borg-Karlson, Namphung Vongvanich, Christer Wiklund. 2007. Male sex pheromone release and female mate choice in a butterfly. Journal of Experimental Biology. 210: 964-970

Romina B. Barrozo, Christophe Gadenne, Sylvia Anton. 2010. Switching attraction to inhibition: mating-induced reversed role of sex pheromone in an insect. Journal of Experimental Biology. 213: 2933-2939

Human Mate Choice: How We Choose Our Mates

Contributed by So Heui Kim

image This black and white photo was created by using the sandwich technique. I randomly chose the faces from a magazine. The third negative is a photo of human cells. My intention was to create a photo that illustrates how our cells and the genes within them are involved in our mate choice.

Despite a lot of interest, it is not clear what traits determine what mates humans choose. It sometimes seems that each individual has different preferences. Humans can be influenced by many factors, including parental guidance, the environment, education, attractiveness, and the media. Some research suggests that despite these influences, human mate choice is based on genetic similarity.

The major histocompatibility complex is believed to take a huge role in human immune system. The MHC molecules bind pathogen-derived peptide fragments and display them on the cell surface to be recognized by the T cells (Janeway, Travers, Walport et al, 2001). These MHC molecules help our body to recognize and eliminate the harmful pathogens. Therefore, maintaining MHC diversity is a key to human survival. The more diversity there are in MHC molecules, the more pathogens will be killed.
In “Major histocompatibility complex peptide ligands as olfactory cues in human body odor assessment”, researchers found out that humans have the ability to detect and evaluate body odor by MHC peptides. In the experiment, human volunteers were asked to apply two different solutions of MHC peptide ligands under their armpits. Then, the participants had to decide which armpit smell they preferred. Participants preferred their body odor more typical of individuals with an MHC profile like their own. This result strongly supports the findings that humans with similar MHC alleles also have similar perfume preference. Unlike when smelling armpits, women prefer the odor of shirts worn by men with different MHC alleles. By mating with a person who has dissimilar MHC genotype, they will maintain their offspring’s MHC diversity.

Wearing perfume is considered one way to attract a mate. Based on the results from the experiments above, we can consider how MHC should impact perfume selection. From the armpit experiment, we can predict that people will prefer to wear perfumes that are similar to their MHC peptides. In “Evidence for MHC-correlated perfume preferences in humans”, researchers found that there is a strong correlation between one’s MHC and their perfume choice. In the first experiment, participants were asked if they liked the smell or not. In a second experiment, participants were asked if they liked the smell, and if they wanted their mates to smell like that. From these experiments, they found out that people sharing specific MHC alleles also share preference for specific perfume odor. In other words, there was a strong correlation between MHC type and one’s preference for the perfume ingredients such as musk, rose, or cardamone. Although this research could not assess which odors were related to MHC, it provides the basis for studies that can test the relationship between the MHC and perfume in more detail. If we can find which odors are related to MHC, we can analyze what perfumes can attract potential mates. If so, we can wear perfumes to not only enhance our body odors, but also to attract our mates.

For more information, please see:

Janeway CA Jr, Travers P, Walport M, et al. Immunobiology: The Immune System in Health and Disease. 5th edition. New York: Garland Science; 2001. The major histocompatibility complex and its functions.

Milinski M, Cory I, Hummel T, Boehm T. 2013 Major histocompatibility complex peptide ligands as olfactory cues in human body odour assessment. Proc R Soc B 280: 20122889.

Milinski M, Wedekind C. 2001 Evidence for MHC-correlated perfume preferences in humans. Behav. Ecol. 12, 140–149.

Sexual Phenomenon as Evidence for the Imperfection in Evolution

Contributed by Sara Allison, Md Saon, Hassan Jassani, Siraj Quad

There is a general misconception that evolution has some sort of directionality associated with it where natural selection pushes organisms only to improve over time towards perfection. The misconception assumes that evolution only produces traits that the organism needs to survive and live long lives. This, however, is not entirely accurate, nor is it the whole story. Natural selection acts on random mutations and selects the ones that best help the organism to survive in a given environment or ones that increase its reproductive fitness. The traits selected for may not be perfect, but are good enough to be maintained through selective pressures. We will focus on a secondary sexual characteristic and sexual cannibalism as evidence for the fact that evolution is not perfect, in that there are not only benefits but also costs for these characteristics.

One example of a trait that is not perfect or optimal for the survival of the organism is the male rhinoceros beetle’s increased horn size. In general, males’ horns tend to be bigger than females’; females prefer males with bigger horns. This trait is not perfect because of the fact that bigger horned rhinoceros beetles experience increased predation, in spite of the trait’s evident advantage when it comes to sexual selection. Thus, the trait is advantageous because it helps males acquire mates and reproduce. However, it is also costly since males with bigger horns have an increased risk of predation. The reason this trait has been favored in spite of its imperfection is because the benefit of big horns being preferred by females outweighs the cost of increased predation through an increase in the number of offspring.


Figure A shows that the big horned male rhinoceros beetle has attracted the female beetle and has a high probability of mating with her—a benefit of big horns. Figure B shows that a smaller horned beetle has failed to attract the same female. Thus, Figure C shows this female fleeing from the small horned beetle without mating with him. Figure D shows that the big horned male receives more predatory attacks than the small horned beetle—a cost to having big horns.

Another example of imperfection in evolution is the evolution of sexual cannibalism, which is an extreme form of sexual conflict that involves the killing and consumption of the mate either before mating or after mating.  It is possible that the occurrence of sexual cannibalism is influenced by low prey availability, which motivates the individual to eat its mate to obtain sustenance—this is known as the foraging hypothesis. Consequent benefits can include an increase in body mass, a healthier body condition, or increased reproductive ability.  A study of the orb-web spider demonstrated that sexual cannibalism increases offspring survival, in which cannibalistic females produced offspring with longer survival times than females that were prevented from consuming their mate.  Although there are benefits, there are also very significant costs. Eliminating the father means a definite loss of any potential paternal care. Additionally, cannibalism can occur before mating and, therefore, cause reproductive failure. In short, the evolution of sexual cannibalism comes with costs and benefits.

The evolution of the big horned male rhinoceros beetle and sexual cannibalism epitomizes the imperfect nature of evolution. Both traits are not perfect in that they come with significant costs. They are maintained because the benefits of each trait outweigh the costs.

For more information, see:

McCullough, Erin L., and Douglas J. Emlen. “Evaluating the costs of a sexually selected weapon: big horns at a small price.” Animal Behaviour 86.5 (2013): 977-985.

Wu, Lingbing, et al. “Factors influencing sexual cannibalism and its benefit to fecundity and offspring survival in the wolf spider Pardosa pseudoannulata (Araneae: Lycosidae).” Behavioral ecology and sociobiology 67.2 (2013):205-212.

Newman, Jonathan A, and Mark AElgar. “Sexual Cannibalism in Orb-Weaving Spiders: An Economic Model.” American Naturalist, The 138.6 (1991):1372-1395.


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Learning in Lizards

Contributed by Elsa Lake

You may have heard about the relative intelligence of some animals, such as dolphins or chimpanzees. However, other animals are not just mechanistic beings. They too have individual variation, including variation in intelligence. An Australian lizard named the Eastern Water Skink (Eulamprus quoyii) was tested for variation in spatial learning performance. An enclosure was set up with a “safe” refuge and an “unsafe” refuge. The lizards were scared around the enclosure until they entered the “safe” refuge. If they entered the “unsafe” refuge, then the refuge was lifted and scaring the lizard resumed.The spatial learning task given to the lizards was learned by twice as many males as females.

Nature presents different challenges to males and females; males are more successful at passing on their genes if they mate with as many different females as possible, and females are more successful if they select males with the highest quality genes to mate with. It is suggested that males have more spatial challenges, such as location of rival males, to deal with, so males would be better at spatial tasks overall.

A Lizard's Dilemma

A “Boldness” Experiment. One refuge was designated the “hot” refuge, and the other the “cold” refuge. Lizards prefer the “hot” refuge because they are cold blooded, and need the external heat to warm up their bodies and get energy, similar to a person who wants to bask in the sun at the beach! However, in the experiment, the lizards were scared off the basking refuge into the “cold” refuge. Researchers measured the time it took for the lizards to return to their basking sites. “Bold” lizards were determined to be those that quickly returned to the basking site, and “shy” lizards took a long time to do so.

The learning task was also more likely to be learned in lizards who were shown to be either very bold or shy, but not likely in lizards with behavior somewhere in between the two extremes. It is suggested that the males in this species of lizard may have evolved so that these two different personalities serve different roles. Territorial lizards are known to actively defend against other males, while “floater” lizards travel from territory to territory in search of mates. These two strategies may be employed by “bold” and “shy” lizards, respectively, while a lizard with a personality in the middle cannot utilize either strategy effectively.


It’s amazing to see how evolution hasn’t caused all Eastern Water Skinks to be the same. There is individual variation in them, just like there is variation in our own personalities. This variation in personality causes us to have different interests, work different jobs, and in general live our lives differently, just as it has caused the male skinks to use different strategies for finding mates. Animals aren’t as different from us as one might think!

See the below papers for more information:

Carazo, P., Noble, D. W. A., Chandrasoma, D., & Whiting, M. J. 2014. Sex and boldness explain individual differences in spatial learning in a lizard. Proceedings of the Royal Society B: Biological Sciences, 281(1782).

Chittka, L., Skorupski, P., & Raine, N. E. 2009. Speed–accuracy tradeoffs in animal decision making. Trends in Ecology & Evolution, 24(7), 400-407.

Noble, D. W. A., Carazo, P., & Whiting, M. J. 2012. Learning outdoors: male lizards show flexible spatial learning under semi-natural conditions. Biology Letters, 8(6), 946-948.

Sih, A., & Del Giudice, M. 2012. Linking behavioural syndromes and cognition: a behavioural ecology perspective. Philosophical Transactions of the Royal Society B: Biological Sciences, 367(1603), 2762-2772.

Stapley, J., & Keogh, J. S. 2004. Exploratory and antipredator behaviours differ between territorial and nonterritorial male lizards. Animal Behaviour, 68(4), 841-846.

Titulaer, M., van Oers, K., & Naguib, M. 2012. Personality affects learning performance in difficult tasks in a sex-dependent way. Animal Behaviour, 83(3), 723-730.

Sexual Evolution of the Cuttlefish

Contributed by Carolyn Barnett, Justin Kim and Mimi Wang

Remember your mom telling you that cheaters never win? Well, she needs to take another look at nature and receive a lesson from the spectacular cuttlefish. Through sexual selection, smaller male cuttlefish, aptly called “sneaker males” have evolved an alternate mating system allowing them to successfully compete with the larger males for mating time. Specifically, the sneaker males take on female coloration, hide their masculine fourth arms, and hold the rest of their arms in the posture of an egg-laying female, in a bid to sidle up to a guarded female.

cuttlefish displays

Cuttlefish display strategies. In the left panel, a sneaker male (center) displays towards the female on the right while not displaying towards the male on his left. In the right panel, there are males on three sides. Rather than try to appear like a female to all of them, the sneaker males chooses to fully display.

Because the sneaker cuttlefish use bright colors to conceal their male features, they are able to avoid aggression from the larger males and increase their chance of mating. Males who know that they can’t win in display or physical combat will sometimes display the brown and white pattern of the female while two other males are fighting over a female.  This allows him to get close to the female and slip her a sperm sac while the other guys are fighting!

Females are the deciding factor on whether or not to accept the males’ advances. In a fertilization study with the cuttlefish, the researchers observed that mimickers succeeded in fertilizing females 60 percent of the time, meaning that this method actually works.

This novel mating system is driven by sexual selection, which is not another term for natural selection. Sexual selection only deals with the driving forces of individuals to increase their reproduction rate, usually by whatever means necessary. In some cases, although the evolved feature may increase their reproduction rate, it can negatively affect their survival. Sneaker cuttlefish use more energy to keep their physical appearance and are more visible in the ocean, which can lead to decreased survival. This disproves the misconception that natural selection works only for the good of the species. If sexual selection allows the animal to reproduce more, the animal accepts that he may have a lower chance of survival.

You may have heard that a big part of evolution is that only the strongest, and largest amongst the population can survive. These cuttlefish show us that you don’t have to be big or strong, you just need to be smarter than the other guys and be fit enough.

For more information, see…

1. It pays to cheat: tactical deception in a cephalopod social signaling system Brown, Garwood, Williamson

2. Adaptive Coloration in Young Cuttlefish (Sepia Officinalis L.): The Morphology and Development of Body Patterns and Their Relation to Behaviour R. T. Hanlon and J. B. Messenger Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences Vol. 320, No. 1200 (Aug. 12, 1988) (pp. 437-487) Page Count: 69 http://www.jstor.org/stable/info/2396667#bibInfo

3. Female impersonation as an alternative reproductive strategy in giant cuttlefish Mark D Norman*, Julian Finn† and Tom Tregenza‡ http://rspb.royalsocietypublishing.org/content/266/1426/1347.short#cited-by

4. Principal features of the mating system of a large spawning aggregation of the giant Australian cuttlefish Sepia apama (Mollusca: Cephalopoda) K. Hall, R. Hanlon http://link.springer.com/article/10.1007/s00227-001-0718-0#

5. Female Choice of Males in Cuttlefish (Mollusca: Cephalopoda) Jean Geary Boal Behaviour, Vol. 134, No. 13/14 (Nov., 1997), pp. 975-988 Published by: BRILL Article Stable URL: http://www.jstor.org/stable/4535485

6. Behavioural and genetic assessment of reproductive success in a spawning aggregation of the Australian giant cuttlefish, Sepia apama Marie-José Naud ,Roger T. Hanlon†, Karina C. Hall‡, Paul W. Shaw§, Jonathan N. Havenhand http://www.sciencedirect.com/science/article/pii/S0003347204000387


The Evolutionary Significance of the Narwhal’s “Tusk”

Contributed by Madeline Haley and Melissa Querrey

First, a short introduction to narwhals by yours truly.


The narwhal, or Monodon monoceros, is a cetacean mammal that inhabits the Arctic waters and is most commonly recognized for its large “tusk”, which closely resembles the horn of the mythical unicorn. Contrary to popular belief, this “tusk” is actually a modified tooth that forms during development from a pair of tooth buds and projects outward from the maxilla, or upper jaw. While both males and females can grow tusks, males tend to have tusks more often than females.

There has been much debate among researchers about the true function of the narwhal’s tusk. It was initially thought that the tusk was only used as an evolutionary means of self-defense and breaking the ice that covers the surface of their aquatic habitats so breaths of air can be taken. However, recent study of the anatomy of the tusk by Nweeia and colleagues revealed nerves that lead directly to the brain, giving evidence of its additional function as a sensory organ.This sensory feature serves several purposes to the narwhal by detecting changes in the external environment, such as salinity and temperature. Because these functions of the narwhal’s tusk increase its chances of survival and are retained in the population, it can be said that they are a result of natural selection.

Additionally, secondary functions of the tusk have developed due to sexual selection, which have facilitated the tusk’s persistence. Based on the discovery of broken tusk fragments and scarring, it can be inferred that male narwhals use their tusk in an aggressive fashion in order to assert sexual dominance and eventually find a mate.

While the narwhal’s tusk may seem like an obnoxious physical display, it is clear that evolutionary forces of both natural and sexual selection have driven the species to utilize its tusk in a way that enables its survival and overall individual and reproductive fitness.

Finally, check out this awesome video about narwhals.

And, for more information:

Palsboll, P.J, Heide-Jorgensen, M.P, & R. Dietz. 1997. Population structure and seasonal movements of narwhals, Monodon monoceros, determined from mtDNA analysis. Heredity 78: 285-292.

Nweeia, M. T., Eichmiller, F. C., Hauschka, P. V., Donahue, G. A., Orr, J. R., Ferguson, S. H., Watt, C. A., Mead, J. G., Potter, C. W., Dietz, R., Giuseppetti, A. A., Black, S. R., Trachtenberg, A. J., & Kuo, W. P. 2014. Sensory ability in the narwhal tooth organ system. The Anatomical Record, 297: 599–617.

Nweeia, M.T., et al. 2009. Considerations of anatomy, morphology, evolution, and function for narwhal dentition. The Anatomical Record 295, 6: 1006-1016.

Silverman, H. B., & M. J. Dunbar. 1980. Aggressive tusk use by the narwhal (Monodon monoceros L.). Nature 284.5751: 57-58.

Brear, K., et al. 1993. The mechanical design of the tusk of the narwhal (Monodon nonoceros: Cetacea). Journal of Zoology 230.3: 411-423.

Mirceta, S., Signore, A.V., Burns, J.M., Cossins, A.R., Campbell, K.L., & Berenbrink, M. 2013. Evolution of Mammalian Diving Capacity Traced by Myoglobin Net Surface Charge. Science 14: 1234192

“Narwhals.” Narwhals. National Geographic, n.d. Web. 18 Apr. 2014.<http://video.nationalgeographic.com/video/narwhals?source=relatedvideo>.



The Mystery of Giraffe Necks

Contributed by Grace Lee

Why do giraffes have long necks? The theory is quite more complicated than expected. Although it’s something that we rarely question, evolutionary scientists have been debating the answer to this question for years. Conveniently, this matter addresses a common theme and misunderstanding of evolutionary biology that we can learn from.

To begin, there are two leading hypotheses as to why giraffes have such long cervical vertebrae. The first, known as the ‘competing browsers’ hypothesis, states that their long necks evolved over time to gain the advantage of being able to reach the leaves of tall trees for feeding. The second, known as the ‘necks for sex’ idea, states that this trait evolved as a weapon that allows males to battle each other to gain dominance for mating with females.

A common misconception is that natural selection produces animals that are perfectly suited for their environment. Unfortunately, evolution does not work to create the “perfection version” of an organism. For example, while it seems that it would be advantageous to have the longest neck in the population, studies show that long necks require increased nutrition for maintenance of health and extreme blood pressures to pump blood from the heart to the brain. Furthermore longer necks may attract predators more easily and may slow down escaping. Evolution is filled with many trade-offs in which a trait is beneficial in one context but harmful in another. There could potentially be a giraffe that not only is suitable for battling rivals and feeding off tall trees but also at the same time easily hidden from predators, but evolution may not necessarily be working towards an “upgrade.”

So what is the correct answer? Perhaps, an unsatisfying “both.” The ‘competing browsers’ idea doesn’t work alone because in the driest seasons, when it would seem the most beneficial to have the longest neck to reach for leaves no other animals could, giraffes tend to feed from shrubs. Even ordinarily, giraffes often feed at shoulder level and “bend over” to do so. The ‘necks for sex’ idea also doesn’t work alone because it doesn’t explain why female giraffes have long necks since they don’t engage in battles for mating.

This returns us to a common theme of evolutionary biology. Evolution is “survival of the fit enough,” more so than “survival of the fittest.” It doesn’t require perfection. Many organisms with varying traits are able to survive and reproduce, and this perhaps leads to the beautifully diversity we see today. The giraffe may not be the perfect organism, but the giraffe is the perfect giraffe.

Check out some of the recent research on Giraffe Necks:

Badlangana, N. L., Justin W. Adams, and Paul R. Manger. 2009. The Giraffe (Giraffa Camelopardalis) Cervical Vertebral Column: A Heuristic Example in Understanding Evolutionary Processes? Zoological Journal Of The Linnean Society 155.3: 736-57.

Mitchell, G., S. J. Van Sittert, and J. D. Skinner. 2009. Sexual Selection Is Not the Origin of Long Necks in Giraffes. Journal of Zoology 278.4: 281-286.

Simmons, R. E., and R. Altwegg. 2010. Necks-for-sex or Competing Browsers? A Critique of Ideas on the Evolution of Giraffe. Journal of Zoology 282.1: 6-12.

Simmons, Robert E., and Lue Scheepers. 1996. Winning by a Neck: Sexual Selection in the Evolution of Giraffe. The American Naturalist 148.5 : 771-786.

Solounias, N. 1999. The Remarkable Anatomy of the Giraffe’s Neck. Journal of Zoology 247.2: 257-268.

Taylor, M. P., D. W. E. Hone, M. J. Wedel, and D. Naish. 2011. The Long Necks of Sauropods Did Not Evolve Primarily through Sexual Selection. Journal of Zoology 285.2 : 150-161.

Wilkinson, David M., and Graeme D. Ruxton. 2011. Understanding Selection for Long Necks in Different Taxa. Biological Reviews: 616-630.