The Evolutionary Response to Unpredictable Environmental Change

Date Published: November 24, 2014

Source: Proceedings of the National Academy of Sciences (PNAS)

Institutions Involved: Department of the Interior Southeast Climate Science Center at North Carolina State University, Department of Biology at Washington University in St. Louis, Centre for Ecological and Evolutionary Studies at the University of Groningen, Centre for Biodiversity Dynamics at Norwegian University of Science and Technology, Department of Ecology, Evolution and Environmental Biology at Columbia University.

Summary:

Variability is becoming more frequent and unpredictable in today’s environment. As a result of this variation in environmental conditions, there is a pressing need for species to cope with and adapt to this phenomenon. Understanding how organisms adapt to changes in their environments is a pivotal idea in evolution and ecology. Evolutionary responses to ecological parameters, such as ambient temperatures or precipitation, can help determine species’ adaptation to environmental change. In a study conducted by Carlos A. Botero, Franz J. Weissing, Jonathan Wright, and Dustin R. Rubenstein, these issues are addressed and analyzed. They study the changes in the predictability of environmental variation that may ultimately affect population feasibility. These biologists develop a model that predicts evolutionary responses to fluctuating environmental conditions and explores the potential consequences of altered environmental cycles. The model indicates that there remains a possibility that fairly large environmental changes can lead to extinction. The model also shows that “parameter space determined by different combinations of predictability and timescale of environmental variation is partitioned into distinct regions where a single mode of response (reversible phenotypic plasticity, irreversible phenotypic plasticity, bet-hedging, or adaptive tracking) has a clear selective advantage over all others”. Furthermore, the model demonstrates that despite evolutionary accommodation, most changes in the environment involve transitions between regions. This, ultimately, can result in rapid population collapse and even extinction. Finally, the model shows that different genetic backgrounds can influence the probability of extinction during such transitions. These insights essentially portray the value of evolutionary thinking in the study of global environmental change. Intrinsically, through evolutionary simulations, these biologists show that adaptive responses consistently evolve under and heavily depend on the different timescales and predictabilities of environmental variation. “Specifically, the potential for adaption to changes in the predictability or timescale of environmental change appears to depend more on the location of parameter space that populations are moving into than on the magnitude of the change itself.” In conclusion, this study helps us expand our understanding of how populations and species may respond to environmental changes and challenges.

Citation:

Botero, C.A., F.J. Weissing, J. Wright, and D.R. Rubenstein. 2014. Evolutionary Tipping Points in the Capacity to Adapt to Environmental Change. Proceedings of the National Academy of Sciences 112:184-189.

Social interaction helps bats decide what to eat

Date Published: July 22, 2014

Source: Behavioral Ecology

Institutions involved: University of Konstanz; Department of Biology, Planck Institute for Ornithology; School of Human Evolution & Social Change; Arizona State University.

Summary: A study conducted by  M. Teague O’Mara, Dina K.N. Dechmann,  and Rachel A. Page  in the Behavioral Ecology journal proposes the possibility of social interaction having a great impact on what food a species of bats decide to eat.

                A study conducted by  M. Teague O’Mara, Dina K.N. Dechmann,  and Rachel A. Page  in the journal of Behavioral Ecology proposes the possibility of social cues having a great impact on what food a species of bats decide to eat. Published July 22, 2012, the journal goes into depth about the different social interactions observed among the Uroderma bilobatum species of bats. Furthermore, several conclusions are drawn about what happens when a bat returns to the roost having eaten a new or novel food.

                Researchers have long hypothesized, and now theorized, that animals have the ability to gather information from other animals that enter or pass by the roost. Although true, what is incredible is not that they have been found to have this ability, but that they can differentiate between reliable and unreliable sources in the form of cues. When individuals come into the roost, they exhibit a sort of signal, or cue, to its roostmates indicating that it had just eaten. These cues could potentially be a change in weight, increased grooming, or odor on breath or fur of the individual. A group of researchers found that these cues can affect the feeding choices of other individuals for a significant amount of time.

               The method involved novel flavored bananas, as the bats are used to a diet of banana. The Uroderma bilobatum were captured and recorded for their mass, forearm length, reproductive status, age, and sex. They were then tagged ad monitored daily for the purpose of their well-being. All of the participants came from the same roost to guarantee their familiarity with one another. The four experiments tested the reaction of bats to novel odor exposure, social information transfer in captivity and in nature, and the ability to discriminate information given by two demonstrators.

               The first experiment conducted by O'Mara and his team involved a dish of novel flavoring mixed with banana that was placed in a mesh enclosure, so that the individual bats could smell but not access it for the purpose of familiarization. The bats were then offered two dishes of food, one with the "familiar" smell and another novel flavored "unfamiliar" dish. In the second experiment, a few bats were taken out of their cage, fed a flavored sugar solution and returned to their cage to eat more bananas. The demonstrator bats were individually given a choice of either bananas with the same novel flavor or a new flavor. The third experiment began with the capture of several free range bats. They were held in a cage and fed a flavored banana-sugar water mixture then freed after two days. The group of researchers then captured members of the roosts they captured the demonstrator bats from and were offered bananas flavored with their demonstrator's flavor or another flavor. In the fourth experiment, O'Mara and his team fed two demonstrators, the first was fed novel-flavored bananas and the second was fed an unflavored sugar solution and then a novel-flavored banana juice mixture was applied to its fur.

                The team found that interaction with a novel food odor wasn't enough for a food bias to form. Furthermore, observer bats were more likely to consume food eaten by demonstrator bats earlier. The fundamental finding is that information gathered from cues was likely to remain in a roost for a few days afterward. This ties into what researchers already know; animals interact and provide one another with information about their environment to continue the struggle to survive.

CITATION:  O'Mara, M.T, D.K.N Dechmann, and R.A Page. 2014. Frugivorous bats evaluate the quality of social information when choosing novel foods. Behavioral Ecology 25(5): 1233–1239.

Evolution of E. coli - Beneficial, or Bearing a Growth Burden?

Date Published:  November 27, 2014

Source:  BMC Evolutionary Biology

Summary:  

Comparative studies over time have lead scientists to conclude that Escherichia coli (E. coli) cells grow larger in size, through generations of evolution. Testing this hypothesis required the collaboration of over 20 scientists. The Department of Infection Metagenomics, at Osaka University, completed the genome analysis component of this study.

The concern regarding E.coli cell growth stems from the fact that cell size is oftentimes proportionate to cell propagation. It could also indicate that there is a greater number of DNA replicating mechanisms in the cell, thus resulting in more frequent cell division. All of these aspects indicate that a larger cell size means a larger growth rate. This increased size does not come without a cost. There is a possibility, as other types of cells have demonstrated, that a segment of the DNA controlling cell division is mutated. Mutations can result in different shapes and sizes that prevent the cell from functioning normally; this is referred to as a growth burden.

Is E. coli in fact growing in size? If it is, what are the growth burdens? To answer this, researchers combined a series of tests. Using E. coli cells, the first test was done to explore whether or not an increase in cell size would hinder replication and growth. Using technology, cells that were smaller than their ancestors were carefully chosen. Scientists noted that a small number of mutations in the membrane-production genes would result in size evolution and no corresponding growth conflict. What initially seemed to be conclusive results actually contained some unforeseen bias. The technology used to select the cells did so in small samples rather than in a large population. Therefore, more tests had to be used in corroboration.

To confirm this, a similar test was done with cells that were thought to evolve towards a smaller sized cell. BSKY, a derived version of E. Coli, was used in this series of complex tests. Throughout, researchers employed a method of examining generations of cells, monitoring cell size and its relation to density. The cells thought to behave in this way did so regardless of the cell concentrations. In addition to these tests, genome sequencing was necessary to confirm mutations in genes coding for growth rates.

Results confirmed that a growth disadvantage does not directly link to cell size increase. RE Lenski, one of the key researchers in this study, conducted these experiments. In fact, we also see the significance behind the short time span needed for bacterial cell size to evolve. It is clear that cell size holds an important part in survival rates. A cell is less prone to external attack from protists if they are large and have a thick cell membrane. This is one of the results of evolutionary cell size increase. Evolution of cell size may be another form of natural selection, or survival of the fittest.

The diagram above depicts concentration versus time. ACs, T22Cs, Svr22Cs, and Mld22Cs are sample cells that behave similar to E. Coli. Thus, they were used in the empirical studies. They demonstrate a proportional growth rate despite the fact hat their concentration is increasing. As time goes on, their size has evolved as well, without any visible growth burden.

In conclusion, we can see that bacterial cell size evolution is a quick process that occurs in under 400 generations. Because of logistical limitations, scientists used “an empirical method” to test this. Cells thought to decrease in size demonstrated stringent selection, resulting in smaller subsequent generations. They shrunk without any disadvantage to the cell’s fitness. Thus, it can be pragmatically stipulated that E. coli cells are capable of evolving to become larger, without sacrificing fitness.

Citation:

Mari, Y., Saburo, T., Naoko, H., Shigeto, S., Hideo, M., Bei-Wen, Y., & Tetsuya, Y. (2014). Directed evolution of cell size in Escherichia coli. BMC Evolutionary Biology, 14(1), 104-127. doi:10.1186/s12862-014-0257-1

Social and Ecology factors Influencing offsprings survivals

Date Published: October 17, 2014

Source: Behavioral Ecology: International Society for Behavioral Ecology

Summary:  This article illustrates how reproductive success is directly correlated to interactions amongst other fetuses as well as offsprings and other social and ecological factors. Essentially, reproductive success or fitness is classified by how many offsprings an organism can have and of those offsprings how many actually survive and create a new generation. The article highlights that many studies solely focus on either the pre natal stages or the post natal stages of an organism however its imperative to understand that it they are both intertwined and interdependent.

One of the major factors that are well known is the effect climate has on the survival of offsprings. When there is plentiful rainfall, the result is higher plant productivity, which then increases food availability. This is important when considering the health of the mother but also each of the offsprings since they will have lots of food available and there isn’t competition in regards to food. When thinking of the social aspect, this article shows that though females may have a certain amount of conflict and competition amongst each other, there is safety in numbers. Living with other females that have offsprings allows there to be more resources and more protection. This again increases the chances of survival. These are only a few basic examples of ecological and social factors influencing the fitness of a species.

The main idea of this study was to research and ecological and social factors that were prevalent in pre and postnatal offsprings which lead to the survival of macaques located in Sulawesi. The reason why this specie was chosen for this experiment is because they have an evident percent of infant mortality and there low predation pressure. Also this specie gives birth year rounds so the data flow would be constant. The experiment was conducted where the climate stay relatively constant through out the year. The rainfall was above average for this specie to survive. They tested their predictions with three groups over the span of 152 months.

The results that were collected conclude that social variables explain the survival rate because the more encounters the fetuses were involved in, the more likely they were to survive. This was unexpected because the prediction was that more encounters would encourage competition and add stress to the female decreasing the survival rate. The study did support the hypothesis that the environment also plays a role especially when talking about rainfall. Rainfalls lead to a greater among of fruits available, which lead to a healthier diet for both mother and offsprings. It was also noted that if the mother was presented, their offsprings would be more likely to survive because females were more aggressive in their means of protection. From this study, it can be summarized that ecological and social factors due influence fitness seen through the macaques species.


Citation: 

Daphne Kerhoas, 

Dyah Perwitasari-Farajallah, 

Muhammad Agil, 

Anja Widdig and 

Antje Engelhardt, Behavioral Ecology (2014) 25 (5): 1164-1172 doi:10.1093/beheco/arue099

1. 
   

The affect of monitoring costs on prey flee distance

Economic escape theory states that there exist several relationships between flight-initiation distance (FID, the distance between a predator and its prey when the prey begins to flee) and the cost of fleeing. However, the theory fails to explain why FID increases as starting distance (SD, the distance between predator and prey when the predator begins to approach) increases. A study published by Behavioral Ecology and conducted by William E. Cooper Jr. from Indiana University-Purdue University and Daniel T. Blumstein from University of California at Los Angeles proposes that this phenomenon is caused by costs involving the monitoring of the predator during predation.

The researchers collected data from 76 avian species and recorded changes in basal metabolic rate (BMR) when the prey first became aware of the predators. They measured differences in BMR in response to alert distance (AD, the distance at which the prey first becomes aware of its predator), as well as SD and FID. The proposed hypothesis was that when SD and AD were higher, the prey would need to spend more time monitoring the predator, and this physiological cost of heightened awareness would cause the prey to have an increased FID, since fleeing as soon as possible would minimize the amount of biological resources consumed.

The results were in accordance with the hypothesis. The researchers found that during instances of high SD and AD, the FID was also higher, and BMRs were relatively high. This led the researchers to conclude that monitoring costs negatively influenced the FID, but only when the FID was found to be large. In instances of low FID, they concluded that BMR and cost of monitoring could not have any substantial relationship, as BMR tends to fluctuate naturally.

These experiments support the original explanation that prey monitoring costs contribute to the apparent starting distance and flight-initiation correlation. More research is needed, however, to confirm that this is the only cause and that there are not any lurking variables. This study is an excellent example of how predator-prey relationships are influenced by a wide array of factors.

Citation:
Cooper, W. E., & Blumstein, D. T. (2014). Novel effects of monitoring predators on costs of fleeing and not fleeing explain flushing early in economic escape theory. Behavioral Ecology, 25(1), 44-52.

The bearings of genetic correlation on the independent evolution of body mass and skeletal dimensions in mammals

Date Published: December 2, 2014

Source: BMC Evolutionary Biology

Summary: Mice were selectively bred to test the hypothesis that a genetic correlation with body and mass compels evolutionary change in the tibia length of mammals. The results of the test showed that the rate of independent evolution of tibia length is hindered by its correlation with body mass (and vice versa).

Mammals typically display a scaling relationship between limb bone size and body mass.

The scaling of limb bone dimensions with body mass ensures proper musculoskeletal function, prevents bones from failing under increased strain from gravity or motion, and serve many other crucial purposes. The correlation between body mass and limb bone dimensions is so significant, in fact, that any major mismatches between the two traits in a populations can have negative impacts on the ability of a mammal to survive (thus, they should be selected against). The exact reason for how the genetic correlation between these two traits impacts a mammal’s ability to evolve independently remains unclear.

The focus of this study was to test the hypothesis that a genetic correlation with body mass constrains evolutionary change in tibia length. Researchers at the University of Calgary in Calgary selectively bred 14 generations of laboratory mice (which came to be known as the Longshanks line) and looked for increases in tibia length independent of body mass.

The results of the experiment showed that tibia length can change quickly and independently from body mass. The quantitative genetic analyses of the test showed that phenotypic correlations were around 0.52, while genetic correlations were 0.4-0.48. In other words, roughly 20% of the genetic variation in tibia length is tied to variation in body mass (the rest of the genetic variance in tibia length evolves independently of body mass). This explains why it responded relatively rapidly to selection and why, over the 14 generations, the mean tibia length increased by 9-13%, while mean body mass remained the same.

This artificial selection experiment exhibited the impact of genetic correlations on the independent evolution of body mass and skeletal size in a mammals. It showed that the independent changes in these complex traits are possible and quick. The results further suggested that the frequent and convergent evolution of relatively longer hind limbs among rodents may also have happened at a quick pace on a geological timescale (possibly due to adaptive radiations, niche partitioning in heterogeneous environments, etc.). Moreover, the simulated evolution indicated that this independent evolution is to some extent compelled by a genetic correlation (which most likely evolved due to natural selection).

Specifically, the experiment displayed that the rate of the independent evolution of tibia length is largely impeded by its correlation with body mass (and vice versa).

Citation:

Marchini, M., Sparrow L. M., Cosman, M. N., Dowhanik, A., Krueger, C. B., Hallgrimsson B., and Rolian, C. 2014. Impacts of genetic correlation on the independent evolution of body mass and skeletal size in mammals. BMC Evolutionary Biology 2014, 14:258 doi:10.1186/s12862-014-0258-0.

Can male fish from distant species attract females with hidden sex signals?

Date Published: September 30, 2013

Source: Behavioral Ecology

Summary: In different species, males and females use different aspects, whether of their physical or mental personalities, to attract the other gender. Their main goal? To reproduce and pass down their genes to future generations. Human males try to use their muscles and good looks to attract females, while male peacocks use their bright colored and large feathers to attract potential female mates. Fish, on the other hand, use specific olfactory sex signals to grab the attention of their fellow female fish. To avoid captivating the attention of females from different species, male fish "typically have high specificity in their signals and are able to distinguish their own signal” from those of other male fish. The fish can discriminate between the signals of other species that live within the area that they are as well inhabiting, however, when a heterospecific male comes, the females may not be able to resist their odor. In the experiment explained in this paper, Rodolphe E. Gozlan, Dean Burnard, J. Robert Britton, and Demetra Andreou, use Pseudorasbora parva and P. promelas to show whether or not females from one species prefer the odor of males from another species that so not originate or inhabit the geographical area that the females do.

In the experiment, all of the fish were kept on the same feeding schedule and after the males and females were isolated from one another for three weeks, all of the fish were isolated in individual plastic planted aerated aquaria. The tanks that held the male fish were placed with a view of the female fish, giving them incentive to produce their odor stimuli. After about twenty four hours, the water containing the odor stimuli were collected from the tanks and used for the experiment. The females that were used for the experiment, not only came from the two different species, but were also divided into two different groups; preovulatory females and postovulatory females. The females were divided into these two specific groups because the “reproductive state of the female influences the response to olfactory sex signals, where preovulatory females show strong behavioral response to male-derived sex cues, whereas postovulatory females do not.”

By using video cameras to observe the female fish, the scientists were able to see that the preovulatory P. parva females preferred the water with the odor of the P. promelas males and that the preovulatory P. promelas females preferred the water with the odor of the P. promelas males. The postvulatory females on the other hand had no preference between the waters of the P. parva males, the P. promleas males, and the controlled water.

Overall the experiment showed how the odor released by the male fish were important for mating selection because of how the postovulatory females (those fish not looking for mates) were not bias to one of the three waters. In addition, the experiment showed that some species of fish, like the P. promelas species, prefer the males of their own species when choosing from the males in their geographical area, but choose males of other species when choosing between males of their own species and males from other geographical locations.

Citation:

Gozlan, R.E., Burnard, D., Britton J.R., and Andreou, D. 2014. Evidence of female preference for hidden sex signals in distant fish. Behavioral Ecology 25: 53-57.