Intrasexual competition among females and the stabilization of a conspicuous colour polymorphism in a Lake Victoria cichlid fish

The maintenance of colour polymorphisms within populations has been a long-standing interest in evolutionary ecology. African cichlid fish contain some of the most striking known cases of this phenomenon. Intrasexual selection can be negative frequency dependent when males bias aggression towards phenotypically similar rivals, stabilizing male colour polymorphisms. We propose that where females are territorial and competitive, aggression biases in females may also promote coexistence of female morphs. We studied a polymorphic population of the cichlid fish Neochromis omnicaeruleus from Lake Victoria, in which three distinct female colour morphs coexist: one plain brown and two blotched morphs. Using simulated intruder choice tests in the laboratory, we show that wild-caught females of each morph bias aggression towards females of their own morph, suggesting that females of all three morphs may have an advantage when their morph is locally the least abundant. This mechanism may contribute to the establishment and stabilization of colour polymorphisms. Next, by crossing the morphs, we generated sisters belonging to different colour morphs. We find no sign of aggression bias in these sisters, making pleiotropy unlikely to explain the association between colour and aggression bias in wild fish, which is maintained in the face of gene flow. We conclude that female-female aggression may be one important force for stabilizing colour polymorphism in cichlid fish.

Age of cichlids: new dates for ancient lake fish radiations

Timing divergence events allow us to infer the conditions under which biodiversity has evolved and gain important insights into the mechanisms driving evolution. Cichlid fishes are a model system for studying speciation and adaptive radiation, yet, we have lacked reliable timescales for their evolution. Phylogenetic reconstructions are consistent with cichlid origins prior to Gondwanan landmass fragmentation 121-165 MYA, considerably earlier than the first known fossil cichlids (Eocene). We examined the timing of cichlid evolution using a relaxed molecular clock calibrated with geological estimates for the ages of 1) Gondwanan fragmentation and 2) cichlid fossils. Timescales of cichlid evolution derived from fossil-dated phylogenies of other bony fishes most closely matched those suggested by Gondwanan breakup calibrations, suggesting the Eocene origins and marine dispersal implied by the cichlid fossil record may be due to its incompleteness. Using Gondwanan calibrations, we found accumulation of genetic diversity within the radiating lineages of the African Lakes Malawi, Victoria and Barombi Mbo, and Palaeolake Makgadikgadi began around or after the time of lake basin formation. These calibrations also suggest Lake Tanganyika was colonized independently by the major radiating cichlid tribes that then began to accumulate genetic diversity thereafter. These results contrast with the widely accepted theory that diversification into major lineages took place within the Tanganyika basin. Together, this evidence suggests that ancient lake habitats have played a key role in generating and maintaining diversity within radiating lineages and also that lakes may have captured preexisting cichlid diversity from multiple sources from which adaptive radiations have evolved.

Preference polymorphism for coloration but no speciation in a population of Lake Victoria cichlids

Female mating preference based on male nuptial coloration has been suggested to be an important source of diversifying selection in the radiation of Lake Victoria cichlid fish. Initial variation in female preference is a prerequisite for diversifying selection; however, it is rarely studied in natural populations. In clear water areas of Lake Victoria, the sibling species Pundamilia pundamilia with blue males and Pundamilia nyererei with red males coexist, intermediate phenotypes are rare, and most females have species-assortative mating preferences. Here, we study a population of Pundamilia that inhabits turbid water where male coloration is variable from reddish to blue with most males intermediate. We investigated male phenotype distribution and female mating preferences. Male phenotype was unimodally distributed with a mode on intermediate color in 1 year and more blue-shifted in 2 other years. In mate choice experiments with females of the turbid water population and males from a clearer water population, we found females with a significant and consistent preference for P. pundamilia (blue) males, females with such preferences for P. nyererei (red) males, and many females without a preference. Hence, female mating preferences in this population could cause disruptive selection on male coloration that is probably constrained by the low signal transduction of the turbid water environment. We suggest that if environmental signal transduction was improved and the preference/color polymorphism was stabilized by negative frequency-dependent selection, divergent sexual selection might separate the 2 morphs into reproductively isolated species resembling the clear water species P. pundamilia and P. nyererei.

Parallel evolution of facial stripe patterns in the Neolamprologus brichardilpulcher species complex endemic to Lake Tanganyika

Colour pattern diversity can be due to random processes or to natural or sexual selection. Consequently, similarities in colour patterns are not always correlated with common ancestry, but may result from convergent evolution under shared selection pressures or drift. Neolamprologus brichardi and Neolamprologus pulcher have been described as two distinct species based on differences in the arrangement of two dark bars on the operculum. Our study uses DNA sequences of the mitochondrial control region to show that relatedness of haplotypes disagrees with species assignment based on head colour pattern. This suggests repeated parallel evolution of particular stripe patterns. The complete lack of shared haplotypes between populations of the same or different phenotypes reflects strong philopatric behaviour, possibly induced by the cooperative breeding mode in which offspring remain in their natal territory and serve as helpers until they disperse to nearby territories or take over a breeding position. Concordant phylogeographic patterns between N. brichardi/N. pulcher populations and other rock-dwelling cichlids suggest that the same colonization routes have been taken by sympatric species and that these routes were affected by lake level fluctuations in the past. (C) 2007 Elsevier Inc. All rights reserved.

Characterization of legacy organic carbon in a culturally eutrophic lake : the role of the historic carbon deposition in the time course and extent of lake recovery

The time course of lake recovery after a reduction in external loading of nutrients is often controlled by conditions in the sediment. Remediation of eutrophication is hindered by the presence of legacy organic carbon deposits, that exert a demand on the terminal electron acceptors of the lake and contribute to problems such as internal nutrient recycling, absence of sediment macrofauna, and flux of toxic metal species into the water column. Being able to quantify the timing of a lake’s response requires determination of the magnitude and lability, i.e., the susceptibility to biodegradation, of the organic carbon within the legacy deposit. This characterization is problematic for organic carbon in sediments because of the presence of different fractions of carbon, which vary from highly labile to refractory. The lability of carbon under varied conditions was tested with a bioassay approach. It was found that the majority of the organic material found in the sediments is conditionally-labile, where mineralization potential is dependent on prevailing conditions. High labilities were noted under oxygenated conditions and a favorable temperature of 30 °C. Lability decreased when oxygen was removed, and was further reduced when the temperature was dropped to the hypolimnetic average of 8° C . These results indicate that reversible preservation mechanisms exist in the sediment, and are able to protect otherwise labile material from being mineralized under in situ conditions. The concept of an active sediment layer, a region in the sediments in which diagenetic reactions occur (with nothing occurring below it), was examined through three lines of evidence. Initially, porewater profiles of oxygen, nitrate, sulfate/total sulfide, ETSA (Electron Transport System Activity- the activity of oxygen, nitrate, iron/manganese, and sulfate), and methane were considered. It was found through examination of the porewater profiles that the edge of diagenesis occurred around 15-20 cm. Secondly, historical and contemporary TOC profiles were compared to find the point at which the profiles were coincident, indicating the depth at which no change has occurred over the (13 year) interval between core collections. This analysis suggested that no diagenesis has occurred in Onondaga Lake sediment below a depth of 15 cm. Finally, the time to 99% mineralization, the t99, was viewed by using a literature estimate of the kinetic rate constant for diagenesis. A t99 of 34 years, or approximately 30 cm of sediment depth, resulted for the slowly decaying carbon fraction. Based on these three lines of evidence , an active sediment layer of 15-20 cm is proposed for Onondaga Lake, corresponding to a time since deposition of 15-20 years. While a large legacy deposit of conditionally-labile organic material remains in the sediments of Onondaga Lake, it becomes clear that preservation, mechanisms that act to shield labile organic carbon from being degraded, protects this material from being mineralized and exerting a demand on the terminal electron acceptors of the lake. This has major implications for management of the lake, as it defines the time course of lake recovery following a reduction in nutrient loading.

Open top chambers and infrared lamps : a comparison of heating efficacy and CO₂/CH₄ dynamics in a Lake Superior coastal peatland

Experimental warming provides a method to determine how an ecosystem will respond to increased temperatures. Northern peatland ecosystems, sensitive to changing climates, provide an excellent setting for experimental warming. Storing great quantities of carbon, northern peatlands play a critical role in regulating global temperatures. Two of the most common methods of experimental warming include open top chambers (OTCs) and infrared (IR) lamps. These warming systems have been used in many ecosystems throughout the world, yet their efficacy to create a warmer environment is variable and has not been widely studied. To date, there has not been a direct, experimentally controlled comparison of OTCs and IR lamps. As a result, a factorial study was implemented to compare the warming efficacy of OTCs and IR lamps and to examine the resulting carbon dioxide (CO2) and methane (CH4) flux rates in a Lake Superior peatland. IR lamps warmed the ecosystem on average by 1-2 #°C, with the majority of warming occurring during nighttime hours. OTC's did not provide any long-term warming above control plots, which is contrary to similar OTC studies at high latitudes. By investigating diurnal heating patterns and micrometeorological variables, we were able to conclude that OTCs were not achieving strong daytime heating peaks and were often cooler than control plots during nighttime hours. Temperate day-length, cloudy and humid conditions, and latent heat loss were factors that inhibited OTC warming. There were no changes in CO2 flux between warming treatments in lawn plots. Gross ecosystem production was significantly greater in IR lamp-hummock plots, while ecosystem respiration was not affected. CH4 flux was not significantly affected by warming treatment. Minimal daytime heating differences, high ambient temperatures, decay resistant substrate, as well as other factors suppressed significant gas flux responses from warming treatments.

Modeling contaminant behavior in Lake Superior : a comparison of PCBs, PBDEs, and mercury

A mass‐balance model for Lake Superior was applied to polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), and mercury to determine the major routes of entry and the major mechanisms of loss from this ecosystem as well as the time required for each contaminant class to approach steady state. A two‐box model (water column, surface sediments) incorporating seasonally adjusted environmental parameters was used. Both numerical (forward Euler) and analytical solutions were employed and compared. For validation, the model was compared with current and historical concentrations and fluxes in the lake and sediments. Results for PCBs were similar to prior work showing that air‐water exchange is the most rapid input and loss process. The model indicates that mercury behaves similarly to a moderately‐chlorinated PCB, with air‐water exchange being a relatively rapid input and loss process. Modeled accumulation fluxes of PBDEs in sediments agreed with measured values reported in the literature. Wet deposition rates were about three times greater than dry particulate deposition rates for PBDEs. Gas deposition was an important process for tri‐ and tetra‐BDEs (BDEs 28 and 47), but not for higher‐brominated BDEs. Sediment burial was the dominant loss mechanism for most of the PBDE congeners while volatilization was still significant for tri‐ and tetra‐BDEs. Because volatilization is a relatively rapid loss process for both mercury and the most abundant PCBs (tri‐ through penta‐), the model predicts that similar times (from 2 ‐ 10 yr) are required for the compounds to approach steady state in the lake. The model predicts that if inputs of Hg(II) to the lake decrease in the future then concentrations of mercury in the lake will decrease at a rate similar to the historical decline in PCB concentrations following the ban on production and most uses in the U.S. In contrast, PBDEs are likely to respond more slowly if atmospheric concentrations are reduced in the future because loss by volatilization is a much slower process for PBDEs, leading to lesser overall loss rates for PBDEs in comparison to PCBs and mercury. Uncertainties in the chemical degradation rates and partitioning constants of PBDEs are the largest source of uncertainty in the modeled times to steady‐state for this class of chemicals. The modeled organic PBT loading rates are sensitive to uncertainties in scavenging efficiencies by rain and snow, dry deposition velocity, watershed runoff concentrations, and uncertainties in air‐water exchange such as the effect of atmospheric stability.

Tracing the source of groundwater for three different coastal peatlands along Lake Superior

The goal of this project was to investigate the influence of a large inland lake on adjacent coastal freshwater peatlands. The specific aim was to determine the source of groundwater for three differently formed peatlands located on the southern shore of Lake Superior. The groundwater study was conducted at Bete Grise, a peatland complex in a dune-swale system; Pequaming, a peatland developed in the swale of a tombolo; and Lightfoot Bay, a peatland developed in a barrier beach wetland complex. To determine the source of groundwater in the peatlands, transects of six groundwater monitoring wells were established at each study site, covering distinctly different vegetation zones. At Pequaming and Lightfoot Bay the transects monitored two vegetation zones: transition zone from upland and open fen. At Bete Grise, the transects monitored dunes and swales. Additionally, at all three sites, upland groundwater was monitored using three wells that were installed into the adjacent upland forest. Biweekly measurements of well water pH and specific conductance were carried out from May to October of 2010. At each site, vegetation cover, peat depths and surface elevations were determined and compared to Lake Superior water levels. From June 14 – 17, July 20 – 21 and September 10 – 12, stable isotopes of oxygen (18O/16O) ratios were measured in all the wells and for Lake Superior water. A mixing model was used to estimate the percentage of lake water influencing each site based on the oxygen isotope ratios. During the sampling period, groundwater at all three sites was supported primarily by upland groundwater. Pequaming was approximately 80 % upland groundwater supported and up to 20 % Lake water supported in the uppermost 1 m layer of peat column of the transition zone and open fen. Bete Grise and Lightfoot Bay were 100 % upland groundwater supported throughout the season. The height of Lake Superior was near typical levels in 2010. In years when the lake level is higher, Lake water could intrude into the adjacent peatlands. However, under typical hydrologic conditions, these coastal peatlands are primarily supported by upland groundwater.

Ecology of larval fishes and large zooplankton in the Keweenaw Current region of Lake Superior, with special focus on lake herring, Coregonus artedi

I assessed the influence of the Keweenaw Current and spring thermal bar on the distribution of larval fishes and large zooplankton in Lake Superior. In 1998 and 1999, samples were collected from inshore (0.2 – 3.0 km from shore) and offshore (5.0 – 9.0 km from shore) locations on three transects off the western coast of the Keweenaw Peninsula, Michigan. For larval fishes, density and size distribution patterns of lake herring (Coregonus artedi), rainbow smelt (Osmerus mordax), burbot (Lota lota), deepwater sculpin (Myoxocephalus thompsoni), and spoonhead sculpin (Cottus ricei) suggest a seasonal inshore to offshore movement. For zooplankton, seasonal warming appeared to be the major factor that limited planktonic catches of the primarily benthic Mysisrelicta and Diporeia spp., while simultaneously stimulated growth and reproduction of the cladocerans Daphnia spp., Holopedium gibberum, and Bythotrephes cederstroemi. In contrast, calanoid copepods as a group were abundant throughout the entire sampling season. The greatest abundances of zooplankton were generally encountered offshore, even for the cladocerans, which apparently expanded from inshore to offshore locations with seasonal warming. In 2000, sampling efforts focused on lake herring. Samples were collected from surface waters at 0.1 – 17.0 km from shore on two transects. Lake herring larvae were also reared in the laboratory from eggs in order to validate the use of otolith microstructure for aging. Increment deposition was not statistically different from a daily rate starting from 28 days after hatching, near the time of yolk-sac absorption, but larvae with lower growth rates could not be aged as accurately. In Lake Superior, lake herring tended to be slightly more abundant, larger, and older at inshore locations, but a dense patch of younger larvae was also encountered 7 – 13 km from shore. The distribution iiipatterns suggest that larvae were transported by prevailing currents into the study region, possibly from the more productive spawning regions in western Lake Superior. Growth rates were suppressed at offshore locations where temperatures were less than 8°C. These results indicate that lake herring larvae may be transported far distances from spawning concentrations by longshore currents, and water temperatures may largely control their growth.

Public preferences of the Great Lakes Environment : a Lake Michigan pilot study

The Great Lakes watershed is home to over 40 million people, and the health of the Great Lakes ecosystem is vital to the overall economic, societal, and environmental health of the U.S. and Canada. However, environmental issues related to them are sometimes overlooked. Policymakers and the public face the challenges of balancing economic benefits with the need to conserve and/or replenish regional natural resources to ensure long term prosperity. From the literature review, nine critical stressors of ecological services were delineated, which include pollution and contamination, agricultural erosion, non-native species, degraded recreational resources, loss of wetlands habitat, climate change, risk of clean water shortage, vanishing sand dunes, and population overcrowding; this list was validated through a series of stakeholder discussions and focus groups in Grand Rapids. Focus groups were conducted in Grand Rapids to examine the awareness of, concern with, and willingness to expend resources on these stressors. Stressors that the respondents have direct contact with tend to be the most important. The focus group results show that concern related to pollution and contamination is much higher than for any of the other stressors. Low responses to climate change result in recommendations for outreach programs.