Female butterflies have no trouble breeding despite shortage of males

In a recent study, researchers have discovered that female monarch butterflies, also known as African queens, are remarkably adept at finding mates, even in populations where a male-killing parasite has significantly reduced the number of males. 

The study, led by scientists from the University of Exeter, University of Edinburgh, and the Dian Fossey Gorilla Fund, sheds light on the mating behavior of these butterflies and the implications for their survival.

Spiroplasma, a parasite that some female butterflies carry, kills all their male offspring, leading to highly infected populations with very few males. Despite this, the researchers found that females mated about 1.5 times on average, irrespective of the number of males present. 

In some cases, the male proportion dropped below 10 percent. However, the remaining males appeared to successfully breed with most of the available females. Only 10-20 percent of female butterflies remained unmated. This figure is only slightly higher than the expected average in a population with plenty of males (5-10 percent).

Vincent Rutagarama, a student at the University of Rwanda and the study’s first author, described the experience of working with an international team of experts as “inspiring and powerful.” He believes the knowledge gained from this research will shape his future career path towards research-based conservation.

Female butterflies breeding success

Professor Richard ffrench-Constant is from the Centre for Ecology and Conservation at Exeter’s Penryn Campus in Cornwall. He noted the consistency of female butterflies’ breeding success throughout the year. This occurs despite fluctuations in the proportion of males in butterfly populations. 

Dr. Ian Gordon from the University of Rwanda suggested that this breeding success might explain how the male-killing parasite could transmit successfully in populations where males are rare.

Dr. Gordon highlighted the irony of the situation: if the entire population were infected, monarch butterflies would produce no more princes, and both the parasite and the butterflies would die out. Further research is needed to understand why some monarch female butterflies remain uninfected and can produce healthy male offspring. 

Additional studies may also investigate why the male-killing parasite is currently confined to a sub-section of the East African ‘contact zone.’ This is where prevailing winds converge and bring flying insects together.

Female butterflies evolving resistance to parasites

According to Professor ffrench-Constant, other butterfly species have evolved resistance to parasites like Spiroplasma. Monarchs, which are numerous and widespread, are unlikely to be at risk. 

However, the researchers expressed concern about the severe drought in East Africa. This has caused a food crisis for humans and damaged biodiversity and ecosystems. They hope that the monarch butterfly can become a symbol of conservation across Africa. The future of monarchs is tied to the future of the continent. Addressing the climate and environment crisis is crucial for its survival.

Researchers conducted the study at sites in Rwanda and Kenya. It involved counting male-female ratios regularly. Scientists also dissected 10 randomly selected female butterflies each month to count spermatophores, which are detectable after breeding. 

The research was funded by the National Geographic Society, Cleveland Metroparks Zoo, and the Dian Fossey Gorilla Fund. The findings have been published in the journal Ecology and Evolution.

More about Monarch butterflies

Monarch butterflies, scientifically known as Danaus plexippus, are among the most recognizable and iconic butterfly species. This is due to their striking orange, black, and white wing patterns. They are native to North and South America. Their range also extends to other parts of the world, including Australia, New Zealand, and some Pacific islands. Monarchs are known for their incredible long-distance migration. This is unique among butterflies.

Migration

Monarch butterflies are famous for their annual migration, which can cover thousands of miles. In North America, they travel from their breeding grounds in the United States and southern Canada to their wintering sites in central Mexico. This journey can span over 3,000 miles and takes several generations of monarchs to complete. The butterflies that migrate to Mexico are the fourth generation of the year. They are the ones that make the return journey to the United States and Canada in the spring.

Life Cycle

The monarch butterfly’s life cycle consists of four stages: egg, larva (caterpillar), pupa (chrysalis), and adult. The entire life cycle takes about a month to complete, with the adult stage lasting for 2-6 weeks. Female monarchs lay their eggs on milkweed plants, which serve as the primary food source for monarch caterpillars. The caterpillar stage lasts about 10-14 days. After this, the caterpillar forms a chrysalis, where it undergoes metamorphosis into an adult butterfly over the next 10-14 days.

Diet

As caterpillars, monarchs feed exclusively on milkweed plants (genus Asclepias). Milkweed contains toxic compounds called cardenolides, which the caterpillars store in their bodies, making them unpalatable to predators. This defense mechanism carries over to the adult stage, where the bright orange and black colors of the monarch butterfly serve as a warning to predators that they are toxic. Adult monarchs feed on nectar from a variety of flowers, providing them with the energy necessary for flight, reproduction, and migration.

Conservation

Monarch butterflies face several threats, including habitat loss, climate change, and the widespread use of pesticides. Experts have linked the decline in monarch populations to the loss of milkweed plants, in particular. They are vital to the butterflies’ life cycle. Researchers have initiated Conservation efforts to protect and restore monarch habitats. These efforts also encourage the planting of milkweed and reducing pesticide use. These efforts aim to ensure the long-term survival of this iconic species and the important role they play in pollination and as indicators of ecosystem health.

Climate change and the global butterfly population

Climate change is impacting the global butterfly population in several ways. Changes in temperature, precipitation patterns, and the frequency of extreme weather events drive the most significant effects.

These changes can lead to alterations in the distribution, abundance, and behavior of butterfly species, with potential consequences for ecosystem health and biodiversity. Some of the key ways climate change is affecting butterflies include:

Range shifts

As temperatures rise, many butterfly species are moving to higher elevations or latitudes in search of more suitable habitats. This can lead to changes in the distribution of species and the potential for local extinctions in areas where they can no longer survive. In some cases, species may expand their ranges into new areas, increasing the potential for competition with native species and disruptions to local ecosystems.

Phenology changes

Phenology refers to the timing of biological events, such as the emergence of adult butterflies or the flowering of plants. Climate change can alter the phenology of butterflies, leading to mismatches between their life cycles and the availability of resources, such as food plants for caterpillars or nectar sources for adults. Such mismatches can negatively impact butterfly populations, as they may struggle to find enough food to support their growth and reproduction.

Population declines

Changes in temperature and precipitation patterns can lead to declines in butterfly populations, particularly for species that are sensitive to environmental changes or have specialized habitat requirements. Additionally, extreme weather events, such as droughts, floods, or heatwaves, can cause direct mortality or disrupt the availability of resources that butterflies depend on, further contributing to population declines.

Loss of genetic diversity

As butterfly populations decline and become more fragmented, they may lose genetic diversity, making them more vulnerable to extinction. Smaller populations are more susceptible to inbreeding, which can reduce their ability to adapt to changing environmental conditions.

Changes in community composition

Climate change can lead to shifts in the composition of butterfly communities, as some species are more able to adapt to new conditions than others. This can result in a loss of biodiversity and alter the ecological roles that butterflies play, such as their contributions to pollination and their function as prey for other species.

Overall, climate change presents significant challenges for the conservation of global butterfly populations. Efforts to mitigate climate change and protect butterfly habitats are essential for ensuring the long-term survival of these important and diverse organisms.

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