Image Credit: Green News Ireland
As the world celebrated Earth Day earlier this week, New York joined California and Hawaii in legally banning single-use plastic bags! In a country obsessed with plastic, this represents a major victory for the environmental movement. According to an article in Forbes, "In 2014 it is estimated that the United States used 100 billion single-use plastic shopping bags with the average American family using 1,500 single-use plastic bags each year." That is an astronomical amount of plastic making its way into landfills, parks, oceans, even the air - and those numbers don't even consider the other sources of plastic contamination, With three states leading the charge, I can only hope/imagine that more states will follow with similar bans.
We've known about the dangers of plastics for years. Back in February 2015, I wrote an article on the realities plastic (and other) waste impose on marine mammals. Four years later, this article is still frighteningly relevant. I posted it below with minor modifications, but want to emphasize the victories (like the plastic bag ban!) that have occurred since its initial publication in the Columbia Science Review. I am confident more victories will follow, and encourage everyone (myself included!) to continually find ways that we can all decrease plastic use in our every day lives.
By Alexandra DeCandia
Humans have a love affair with plastic. Lightweight, versatile, durable, and inexpensive synthetic polymers have flooded the global market since 1950. Yet the qualities that earn success in the marketplace also severely endanger the natural environment. Winds, rivers, and currents carry lightweight refuse ocean-bound, where cooler temperatures and UV-protection render it long lasting. Plastic floats in bodies of water for decades before degrading into “microplastics,” with these miniscule particles posing additional risks to ocean life. They mingle with professional fishing gear and “ghost nets” that wander around the ocean silently seizing marine mammals. Amid this plastic, limbs get entangled, digestive tracts occluded, and tissues infused with toxins.
Entanglement occurs when marine mammals are constricted or entrapped by anthropogenic debris. This may lead to strangulation, open sores, impaired behaviors, increased energy expenditure, and, in extreme cases, drowning. New Zealand fur seals, for example, get caught in stray lobster traps but aren’t strong enough to carry them to the surface. Similarly, Dugongs are unable to wriggle free from fishing nets. Even humpback whales, if not freed from tows of nets, ropes, and plastics tangled around their flukes, can die from exhaustion in their struggle to break free. Unfortunately, ocean debris acts as an anchor for these trapped animals. Even stray monofilament lines can lock animals down to the ocean floor.
Old fishing gear abandoned in the ocean can lead to entanglement. Image Credit: NOAA
The second threat stemming from the misuse of plastics is ingestion, and occurs when organisms mistake debris for food. Plastics come in all shapes, sizes, and colors, so plastic debris can mimic the look of mammalian food. Analysis of polar bear scat, for instance, revealed ingestion of debris like foil, cardboard, cigarette butts, duct tape, foam rubber, glass, paint chips, paper, plastic, wood, and even a watch band. While these items passed through the animal, others often get stuck. And since synthetic materials do not degrade as organic ones do, ingestion can yield wounds internally and externally, gastro-intestinal blockages, false sensations of satiation, toxin bioaccumulation in tissues, impaired feeding capability, and even starvation. In 2008, examination of the stomach contents of two sperm whales stranded in northern California uncovered ropes, plastics, and 134 different types of fishing nets. One whale died of a ruptured stomach; the other of starvation. Both deaths were directly caused by debris ingestion.
Marine mammals are fairly diverse, so often times the distinct behaviors, morphologies, and habitat requirements render certain risks more threatening to one type of organism over another. The order Carnivora, which contains polar bears, sea otters, and pinnipeds, dwell at the intersection of land and sea. These animals seem to approach their dual environments with a sense of curiosity. As a result, marine debris poses a particular risk of entanglement as they excitedly explore their surroundings. Pinnipeds are drawn to novel items such as plastic bags or abandoned nets, and accidentally slip their heads inside loops and holes. Then, since the animal is unable to escape, these “lethal necklaces” remain on their necks, constricting the animal as it grows.
For some species, such as critically endangered Hawaiian monk seals, entanglement has been implicated as a major threat to population growth. Even a seemingly modest rate of entanglement of 0.04%-0.78% has proven detrimental to an ailing population.
Many mammals mistake plastics for food. Image Credit: The Times
The order Cetacea consists of mysticetes (baleen whales) and odontocetes (toothed whales). Unlike pinnipeds, cetaceans are entirely marine, large bodied, and migratory. Ingestion is among the greatest threats to these animals. Nets and plastics can tangle around their bodies and prevent them from feeding. On a smaller scale, microplastics join the krill that these animals ingest or skim on the surface. When the animals filter feed, synthetic particulates enter their bodies and bioaccumulate. In the case of Mediterranean fin whales, these plastics leech toxins into their tissues. Odontocetes largely avoid these risks associated with filter feeding. However, their large-scale ingestion of marine debris does cause plastic impaction, gastro-intestinal tract blockages, starvation, and gastric rupture.
The final order, Sirenia, contains dugongs and manatees. Like cetaceans, sirenians spend their entire lives submerged beneath the waves of aquatic environments. Unlike cetaceans, they travel through coastal waters, estuaries, and inland river networks. While herbivory precludes the risk of bioaccumulation through feeding, entanglement and ingestion still pose a threat to these species.
When we think about the popularity of plastics in our society, it seems that the threat of entanglement and ingestion is inevitable. However, through the implementation of stringent legislation, recycling initiatives, incentive programs, consumption reductions, and citizen-led clean up efforts, this does not have to be the case. Education, activism, and compliance on our part can go a long way. While the ocean will never be completely devoid of plastic, we can prevent further degradation from this point forward. Through increased awareness, it is possible that marine mammals won’t have to live in an environment inundated by trash.
Photo credit: © L. Hamelbeck‐Galle/stadtwildtiere.at
A few weeks ago, I wrote a post for the Ecology and Evolution Blog about a recent paper I published with a fantastic team of collaborators! We looked at red foxes colonizing Zurich, Switzerland to better understand the genetic consequences of urban colonization. For the blog post, see below. For our publication in Ecology and Evolution, click this link.
By Alexandra DeCandia
True to its name, the Anthropocene is characterized by human-mediated environmental change on a global scale. Currently, over 7.7 billion humans reside on our planet, 55% of whom live in cities. As a result, an estimated 3% of earth’s land surface is considered urbanized, with all of these values expected to increase in the next century .
As natural lands are coopted for human habitation and resource production, wildlife are left with three options :
In each case, urbanization can raise conservation concerns or increase the potential for human-wildlife conflict. Thus, understanding the ecology and evolution of urban wildlife systems becomes critical for peaceful and long-term coexistence between humans and our neighboring wildlife.
Red foxes (Vulpes vulpes) are an ideal study system for examining the effects of urban wildlife colonization. These flexible, mid-sized carnivores are capable of thriving in diverse habitats from natural landscapes through dense city centers . Found across the northern hemisphere, urban fox colonization is especially pronounced in Europe, where foxes have successfully colonized cities since the 1930s. Aspects of their ecology, such as dietary preferences, disease transmission, and movement patterns, have been studied for decades. Yet there are still open questions about the consequences of urban fox colonization, both in terms of ecology and evolution.
Red fox (Vulpes vulpes). Photo credit: © L. Hamelbeck‐Galle/stadtwildtiere.at
To better understand the evolutionary side of things, my collaborators and I set out to characterize the genetic effects of a relatively recent urban colonization event . In the mid-1980s, red fox sightings in Switzerland increased dramatically after rabies was successfully eradicated. As rural populations expanded, more and more foxes moved into the Zurich metropolitan area . Interestingly, movement studies showed that foxes settled in rural and urban areas tended to stay within one habitat type – even if they lived right on the border. That meant that rural foxes typically stayed in rural areas, and urban foxes typically stayed in urban ones.
Since genetics are the raw material of evolution, understanding patterns of genetic diversity in these rural and urban foxes can provide insights into fox demography, colonization history, and chances of long-term survival. Thus in 2003, researchers used eleven neutral markers – or non-coding DNA with no known function – to describe the genetics of this so-called “city fox phenomenon” . They reported decreased genetic diversity in urban foxes, and hypothesized that Zurich was colonized through two independent founder events: one east and one west of Lake Zurich, the Limmat River, and the city center.
Though this study was among the first to examine the genetics of urban colonization, it was unable to consider potential adaptive differences between rural and urban foxes due to its use of neutral genetic markers. This may gloss over functional changes that occur to better suit unique aspects of each environment. For example, city foxes may experience different pressures than rural foxes, such as greater human presence, light and noise pollution, anthropogenic food availability, and disease exposure. Especially if foxes remain localized to one habitat type, these pressures may lead to selection on different behavioral, metabolic, or immune pathways in urban versus rural foxes.
In our study, we revisited the Zurich city fox phenomenon with expanded datasets to consider the neutral and potentially adaptive consequences of urban colonization. We used nine genetic markers linked to functional immune genes and another 10,149 markers found throughout the genome. Our samples included resident foxes living in two urban and three rural locations in the Zurich metropolitan area.
Consistent with previous movement and neutral genetic data, we found evidence of population structure between rural and urban foxes. In essence, foxes sampled in each area were more similar to one another than they were to foxes sampled elsewhere. We also observed that foxes east of the center-city landmarks (i.e., Lake Zurich, the Limmat River, and urban infrastructure) were distinct from foxes sampled to the west. This suggested that foxes don’t often cross those barriers to mate with individuals on the other side.
In addition to population structure, we found decreased diversity in urban foxes when compared to rural foxes. Patterns of diversity at the genome-wide loci suggested a recent genetic bottleneck, whereby a large population quickly reduces in size (as is typical of founder events) and consequently loses variation. (Think of marbles in a bucket: if you have 150 marbles of different colors but only pull out 20 for a small jar, you can’t possibly capture all of the variation of the larger bucket. Genetic bottlenecks work similarly.)
General principle behind genetic bottlenecks. Figure credit: A. L. DeCandia
Despite these diversity losses, we observed evidence for balancing selection (which maintains variation) at markers linked to immune genes. This may be due to the selective advantage that comes from diversity, which can enable better recognition and response to different diseases . We also found a number of genome-wide markers that were associated with urbanization. Interestingly, these markers were found in genes with functions related to metabolism, drug tolerance, immune processes, and colonization relevant behaviors (such as exploration, movement, circadian rhythms, and fear).
These results may suggest local adaptation during urban colonization. As such, they provide a launching point for future studies looking for genes or gene functions that commonly recur across urban colonization events. By examining larger datasets (e.g., full genome sequences) in diverse species (from insects to reptiles to mammals etc.) around the world, we can discover the common ecological and evolutionary processes that characterize urban colonization. We can also identify unique challenges that urban environments pose to wildlife along the urbanophobe to urban exploiter spectrum. This will enable better monitoring and management of urban wildlife populations in the Anthropocene, and facilitate peaceful coexistence with our local wildlife in perpetuity.
Platypus (Ornithorhynchus anatinus) . Photo Credit: https://www.zoo.org.au/melbourne/animals/platypus
In honor of Valentine's Day, I wanted to share an old blog post that I wrote back in college for Columbia Science Review on the bizarre reproductive biology of the platypus. These funky little monotremes have it all: eggs, venomous spurs, cloacas, bifid penises... Dive into the romance of their world...
By Alexandra DeCandia
The platypus (Ornithorhynchus anatinus) is a zoological enigma. One of three extant species in the basal order Monotremata, it exists as an amalgamation of interclass characteristics that engender “Frankenstein’s monster” in taxonomic classification. Particularly in reproductive biology, platypodes blend the structures of mammals, reptiles, and birds to make for some of the strangest sex and reproduction in the animal kingdom.
Unlike most other mammals, platypodes house their reproductive organs within a true cloaca. Retained from reptilian ancestors, this single aperture serves as both the exit point for excretory material and the exchange point for gametes. In females, the cloaca opens into a urogenital sinus that bifurcates into two reproductive tracts. On the left is a functioning ovary; on the right lies a small embryonic sac of primordial follicles. Such asymmetry, while common in many avian and some reptilian species, is rarely exhibited in mammals. It is matched only by the bifid penis of the male, which possesses asymmetrical glands that fit within the female’s uteri in a perfect “lock and key.” To aid fertilization, the upper third of each bifid is covered in keratinized spines that induce ovulation as well as flowery papillae that bring sperm closer to the follicles.
While the bifid, spiny penis is the sexiest of platypus reproductive structures, it is not the only morphology that is a little different in monotreme males. They also possess ascrotal testes that reside within the abdomen. Termed “the testicondid condition,” platypodes are among birds, reptiles, and only a few other mammals that possess this primitive trait. Female platypodes be warned: despite their condition, male monotremes possess some of the largest testes in the world relative to their size. It is thought that sperm competition is likely the culprit. He whose testes are largest, produces the fastest sperm; he whose sperm swims fastest, fertilizes.
Male platypodes do not rely solely on these massive testes to optimize their fitness, though. During breeding season, elevated testosterone levels induce more frequent male-male conflict as breeding partners are sought. Younger, more naïve males choose to adopt stealth as their strategy by exploiting temporal shifts in mate-seeking. Larger, more experienced males utilize battle as means of mate-acquisition. Ornithorhynchus may not appear a fierce warrior with his edentate bill and webbed feet, but with one swift jab of his hind leg, he can incapacitate any enemy long enough for mating to occur. Platypodes possess a venomous spur on the inside of each hind limb. One of the few extant venomous mammals, platypodes can use this nonlethal sting to establish a hierarchy between males and allows only the heartiest competitor to mate.
Courtship in platypodes is brief and pointed. Males, having won the right to approach females unchallenged by subordinates, quickly mate and subsequently leave the inseminated female in search of others. The female, no longer interested in male attention, embarks on her nesting period. In yet another deviation from their mammalian counterparts, platypodes are oviparous. Once eggs reach roughly seventeen millimeters in utero, they exit the female’s cloaca and finish developing on the wet vegetation she deposited in her excavated incubation chamber. Ten days later, the incredibly altricial young use their egg-teeth to liberate themselves from their parchment-shells in order to trade yolk-sacs for milk. Unlike all other mammals, monotremes lack nipples. Therefore, in a touching display of maternal devotion, the female sweats milk from her abdomen so her offspring may suckle and grow.
Lactation lasts for roughly four months. In that time, young platypodes begin to resemble adults and reach a level of self-sufficient maturity befitting adolescents ready to take on the world. Once weaning has occurred with little ado, mother and young depart from the burrow. The males prepare to battle for dominance and inseminate as many females as possible with their keratinized, bifid glans. The females prepare to excavate riverbank burrows, lay eggs from their left uteri, and secrete milk for their young. It’s a unique, ancient strategy of reproduction that has stood the test of time among eutherian mammals alike, despite its strange and haphazard nature. It is successful, it is bizarre, and it is distinctly platypus.