Growth Trendlines

Trendlines help us decide what next steps make the most sense and give a general impression of which conditions yielded healthier plants.

ggplot(sv_ag, aes(
  x = DAS, y = area_cm2, group = interaction(genotype, fertilizer, lex.order = TRUE),
  color = genotype
)) +
  facet_wrap(~ factor(fertilizer, levels = c("0", "50", "100"))) +
  geom_smooth(method = "loess", se = TRUE, fill = "gray90") +
  geom_line(aes(group = barcode), linewidth = 0.15) +
  labs(
    y = expression("Area" ~ "(cm"^2 ~ ")"),
    color = "Genotype"
  ) +
  guides(color = guide_legend(override.aes = list(linewidth = 5))) +
  pcv_theme() +
  theme(axis.text.x.bottom = element_text(angle = 0))

## `geom_smooth()` using formula = 'y ~ x'

Single day comparisons

Non-longitudinal data (or single day data from larger longitudinal data) can be compared using the conjugate function. conjugate uses conjugate priors to make simple Bayesian comparisons for several types of data. Optionally, region of practical equivalence (ROPE) testing is also supported. Most distirubtions supported by this function can be used with either wide or long single value data or wide multi-value data. See ?pcvr::conjugate or the conjugate tutorial for details on usage and available options.

mo17_area <- sv_ag[sv_ag$genotype == "Mo17" & sv_ag$DAS > 18 & sv_ag$fertilizer == 100, "area_cm2"]
b73_area <- sv_ag[sv_ag$genotype == "B73" & sv_ag$DAS > 18 & sv_ag$fertilizer == 100, "area_cm2"]

area_res_t <- conjugate(s1 = mo17_area, s2 = b73_area, method = "t", plot = TRUE, rope_range = c(-5, 5))

Here we can see a dramatic difference in our posterior distributions between genotypes and the distribution of differences between these samples is entirely outside of our ROPE range.

Relative Tolerance

Often bellwether experiments involve comparing stress tolerance between groups. For example in this dataset we might want to know which genotype shows the most resilience to reduced fertilizer. To easily check this we can change out data with relativeTolerance. Details on this function can be read with ?pcvr::relativeTolerance. Note that if you are going to be making a longitudinal model anyway then it makes more sense to use the model to assess relative tolerance rather than transforming data into a different unit.

rt <- relativeTolerance(sv_ag,
  phenotypes = c("area_cm2", "height_cm"),
  grouping = c("fertilizer", "genotype", "DAS"), control = "fertilizer", controlGroup = "100"
)

ggplot(
  rt[rt$phenotype == "area_cm2" & rt$DAS %in% c(10:12), ],
  aes(x = DAS, y = mu_rel, fill = interaction(fertilizer, genotype))
) +
  geom_col(position = "dodge") +
  geom_errorbar(aes(ymin = mu_rel - 1.96 * se_rel, ymax = mu_rel + 1.96 * se_rel),
    position = position_dodge(width = 0.9), width = 0.3
  ) +
  pcv_theme() +
  labs(y = "Relative Tolerance", fill = "Fertilizer\nand Genotype")

Looking at the entire data for the area phenotype is very busy so we might subset to look at something more specific, where we see some odd products of the plants germinating on the bellwether system.

pd <- rt[rt$phenotype == "area_cm2" & rt$DAS %in% c(5:19) & rt$fertilizer == "0", ]
pd$upper_2se <- pd$mu_rel + 2 * pd$se_rel
pd$lower_2se <- pd$mu_rel - 2 * pd$se_rel

ggplot(pd, aes(x = DAS, y = mu_rel, fill = genotype)) +
  geom_col(position = "dodge") +
  geom_errorbar(aes(
    ymin = lower_2se, ymax = upper_2se,
    group = genotype
  ), position = "dodge") +
  pcv_theme() +
  labs(y = "Relative Tolerance")

Cumulative Phenotypes

Sometimes we might want to use the cumulative difference over time

cp <- cumulativePheno(sv_ag, phenotypes = c("area_cm2", "height_cm"), group = "barcode", timeCol = "DAS")

We can check that this worked correctly with trendlines:

ggplot(cp, aes(x = DAS, y = area_cm2_csum, color = genotype, group = barcode)) +
  facet_wrap(~ factor(fertilizer, levels = c("0", "50", "100"))) +
  geom_line() +
  pcv_theme() +
  labs(
    y = expression("Cumulative Sum of Area" ~ "(cm"^2 ~ ")"),
    color = "Genotype"
  )

Longitudinal Modeling

Longitudinal modeling is the most comprehensive way to use the single value traits from a bellwether experiment. Longitudinal modeling can also be complicated compared to single timepoint analyses. Statistical complications including changes in variance, non-linearity, and autocorrelation present potential problems in analyses. To address these we recommend using hierarchical models. pcvr attempts to lower the barrier to entry for these models with helper functions for use with brms, nlme, nlrq, mgcv, and nls. Here we focus only on brms models, but there are tutorials that cover more options.

simdf <- growthSim("logistic",
  n = 20, t = 25,
  params = list("A" = c(200, 160), "B" = c(13, 11), "C" = c(3, 3.5))
)
l <- ggplot(simdf, aes(time, y, group = interaction(group, id))) +
  geom_line(aes(color = group)) +
  labs(title = "Logistic") +
  theme_minimal() +
  theme(legend.position = "none")

simdf <- growthSim("gompertz",
  n = 20, t = 25,
  params = list("A" = c(200, 160), "B" = c(13, 11), "C" = c(0.2, 0.25))
)
g <- ggplot(simdf, aes(time, y, group = interaction(group, id))) +
  geom_line(aes(color = group)) +
  labs(title = "Gompertz") +
  theme_minimal() +
  theme(legend.position = "none")

simdf <- growthSim("monomolecular",
  n = 20, t = 25,
  params = list("A" = c(200, 160), "B" = c(0.08, 0.1))
)
m <- ggplot(simdf, aes(time, y, group = interaction(group, id))) +
  geom_line(aes(color = group)) +
  labs(title = "Monomolecular") +
  theme_minimal() +
  theme(legend.position = "none")

simdf <- growthSim("exponential",
  n = 20, t = 25,
  params = list("A" = c(15, 20), "B" = c(0.095, 0.095))
)
e <- ggplot(simdf, aes(time, y, group = interaction(group, id))) +
  geom_line(aes(color = group)) +
  labs(title = "Exponential") +
  theme_minimal() +
  theme(legend.position = "none")

simdf <- growthSim("linear", n = 20, t = 25, params = list("A" = c(1.1, 0.95)))
ln <- ggplot(simdf, aes(time, y, group = interaction(group, id))) +
  geom_line(aes(color = group)) +
  labs(title = "Linear") +
  theme_minimal() +
  theme(legend.position = "none")

simdf <- growthSim("power law", n = 20, t = 25, params = list("A" = c(16, 11), "B" = c(0.75, 0.7)))
pl <- ggplot(simdf, aes(time, y, group = interaction(group, id))) +
  geom_line(aes(color = group)) +
  labs(title = "Power Law") +
  theme_minimal() +
  theme(legend.position = "none")

(l + g + m) / (e + ln + pl)

priors <- list("A" = 130, "B" = 10, "C" = 0.2)
priorPlots <- plotPrior(priors)
priorPlots[[1]] / priorPlots[[2]] / priorPlots[[3]]

twoPriors <- list("A" = c(100, 130), "B" = c(6, 12), "C" = c(0.5, 0.25))
plotPrior(twoPriors, "gompertz", n = 100)[[1]]

sv_ag$group <- interaction(sv_ag$fertilizer, sv_ag$genotype)

library(brms)
library(cmdstanr)
cmdstanr::install_cmdstan()

ss <- growthSS(
  model = "gompertz", form = area_cm2 ~ DAS | barcode / group, sigma = "spline", df = sv_ag,
  start = list("A" = 130, "B" = 10, "C" = 0.5), type = "brms"
)

ggplot(sv_ag, aes(x = DAS, y = area_cm2, group = barcode, color = group)) +
  geom_line() +
  theme_minimal() +
  labs(
    y = expression("Area" ~ "(cm"^2 ~ ")"),
    color = "Genotype\nand Soil"
  )

fit <- fitGrowth(ss,
  iter = 1000, cores = 2, chains = 2, backend = "cmdstanr",
  control = list(adapt_delta = 0.999, max_treedepth = 20)
) # options to increase performance

brmPlot(fit, form = area_cm2 ~ DAS | barcode / group, df = ss$df) +
  labs(y = expression("Area" ~ "(cm"^2 ~ ")"))

brmViolin(fit, ss, ".../A_group0.B73 > 1.05") +
  ggplot2::theme(axis.text.x.bottom = ggplot2::element_text(angle = 90))

Joyplots

Joyplots are a common way to look at lots of distributions. Here we check the hue histograms as joyplots using three days and add a new fill for the hue colorspace. Joyplots can be made with long or wide multi-value traits.

p <- pcv.joyplot(hue_wide[hue_wide$DAS %in% c(5, 10, 15), ],
  index = "hue_frequencies", group = c("fertilizer", "genotype"),
  y = "DAS", id = NULL
)
p + scale_fill_gradientn(colors = scales::hue_pal(l = 65)(360)) +
  scale_y_discrete(limits = c("5", "10", "15"))

As mentioned previously the conjugate function can be used with wide multi-value data. To use multi value data the samples should be data frames or matrices representing color histograms. Here we compare our color histograms assuming a lognormal distribution and find that they are very similar in this parameterization.

mo17_sample <- hue_wide[
  hue_wide$genotype == "Mo17" & hue_wide$DAS > 18 & hue_wide$fertilizer == 100,
  grepl("hue_freq", colnames(hue_wide))
]
b73_sample <- hue_wide[
  hue_wide$genotype == "B73" & hue_wide$DAS > 18 & hue_wide$fertilizer == 100,
  grepl("hue_freq", colnames(hue_wide))
]

hue_res_ln <- conjugate(
  s1 = mo17_sample, s2 = b73_sample, method = "lognormal",
  plot = TRUE, rope_range = c(-10, 10), hypothesis = "equal"
)

Ordination

Ordinations are another common way to look at multi value traits. The pcadf function runs ordinations and optionally returns the PCs with metadata. Here our simulated data does has a very deterministic pattern due.

pcadf(hue_wide, cols = "hue_frequencies", color = "genotype", returnData = FALSE) +
  facet_wrap(~ factor(fertilizer, levels = c("0", "50", "100")))

Earth Mover’s Distance

Since color data is exported from plantCV as histogram data we can also use Earth Mover’s Distance (EMD) to compare images. Conceptually EMD is a distance that quantifies how much work it would take to turn one histogram into another. Here we do pairwise comparisons of all our rows and return a long dataframe of those distances. Note that even running several cores in parallel this can take a lot of time for larger datasets since the number of comparisons quickly can become unwieldy. The output also will require more work to keep analyzing, so make sure this is what you want to be doing before using EMD to compare color histograms. If you are only interested in a change of the mean then this is probably not the best way to use your data.

Here is a fast example of a place where EMD makes a lot of sense. In this simulated data we have five generating distributions. Normal, Log Normal, Bimodal, Trimodal, and Uniform. We could use some gaussian mixtures to characterize the multi-modal histograms but that will get clunky for comparing to the unimodal or uniform distributions. The conjugate function would not work here since these distributions do not share a common parameterization. Instead, we can use EMD.

set.seed(123)

simFreqs <- function(vec, group) {
  s1 <- hist(vec, breaks = seq(1, 181, 1), plot = FALSE)$counts
  s1d <- as.data.frame(cbind(data.frame(group), matrix(s1, nrow = 1)))
  colnames(s1d) <- c("group", paste0("sim_", 1:180))
  s1d
}

sim_df <- rbind(
  do.call(rbind, lapply(1:10, function(i) {
    simFreqs(rnorm(200, 50, 10), group = "normal")
  })),
  do.call(rbind, lapply(1:10, function(i) {
    simFreqs(rlnorm(200, log(30), 0.25), group = "lognormal")
  })),
  do.call(rbind, lapply(1:10, function(i) {
    simFreqs(c(rlnorm(125, log(15), 0.25), rnorm(75, 75, 5)), group = "bimodal")
  })),
  do.call(rbind, lapply(1:10, function(i) {
    simFreqs(c(rlnorm(100, log(15), 0.25), rnorm(50, 50, 5), rnorm(50, 90, 5)), group = "trimodal")
  })),
  do.call(rbind, lapply(1:10, function(i) {
    simFreqs(runif(200, 1, 180), group = "uniform")
  }))
)

sim_df_long <- as.data.frame(data.table::melt(data.table::as.data.table(sim_df), id.vars = "group"))
sim_df_long$bin <- as.numeric(sub("sim_", "", sim_df_long$variable))

ggplot(sim_df_long, aes(x = bin, y = value, fill = group), alpha = 0.25) +
  geom_col(position = "identity", show.legend = FALSE) +
  pcv_theme() +
  facet_wrap(~group)

Our plots show very different distributions, so we get EMD between our images and see that we do have some trends shown in the resulting heatmap.

sim_emd <- pcv.emd(
  df = sim_df, cols = "sim_", reorder = c("group"),
  mat = FALSE, plot = TRUE, parallel = 1, raiseError = TRUE
)

## Estimated time of calculation is roughly 3.1 seconds using 1 cores in parallel.

sim_emd$plot

Now we can filter edge strength during our network building step for EMD > 0.5, and plot our network.

n <- pcv.net(sim_emd$data, filter = 0.5)
net.plot(n, fill = "group")

The distributions separate very well from each other, but we don’t actually see our uniform distribution here. That is because the uniform distribution does not have self-similar replicates and is also not very similar to the other distributions. If we change our filtering then we can even see which generating distributions are most similar to each other. Here we pass 0.5 as a string, which tells pcv.net to use the top 50 percent of EMD values instead of EMD values > 0.5.

n <- pcv.net(sim_emd$data, filter = "0.5")
net.plot(n, fill = "group")

Just as we’d expect, our uniform distribution shows up now and is the most different. Now changing the edgeFilter in the net.plot function would let us fine tune this plot more to show finer distinctions between our other four generating distributions.

Here is an example of how we might use hue data.

EMD <- pcv.emd(
  df = hue_wide[hue_wide$DAS %in% c(5, 12, 19), ], cols = "hue_frequencies",
  reorder = c("fertilizer", "genotype", "DAS"),
  mat = FALSE, plot = TRUE, parallel = 12, raiseError = TRUE
)

EMD can get very heavy with large datasets. For a recent lemnatech dataset using only the images from every 5th day there were 6332² = 40,094,224 pairwise EMD values. In long format that’s a 40 million row dataframe, which is unwieldy. To get around this problem we might decide to use the hue circular mean as a single value trait or to aggregate some of our data with the mv_ag function.

Starting with our complete hue data we have 1500 image histograms. The mv_ag function will take a group argument and randomly pick members of that group to have their histograms combined. Note that histograms are scaled to sum to 1 before they are sampled. Here we return one example with 2 histograms kept per group and one example where groups are summarized into 1 histogram. If there are equal or fewer images as the n_per_group argument then no aggregation is done for that group but data are rescaled.

hue_ag1 <- mv_ag(df = hue_wide, group = c("DAS", "genotype", "fertilizer"), n_per_group = 2)
dim(hue_ag1)

## [1] 600 183

hue_ag2 <- mv_ag(hue_wide, group = c("DAS", "genotype", "fertilizer"), n_per_group = 1)
dim(hue_ag2)

## [1] 300 183

Network Analysis

As it stands our EMD data is potentially difficult to use for those unfamiliar with distance matrix based analysis. Here we represent our distances as a network to help use the results.

set.seed(456)
net <- pcv.net(EMD$data, meta = c("fertilizer", "genotype", "DAS"), filter = 0.5)

net.plot(net, fill = "DAS", shape = "fertilizer", size = 2)

Our example network shows some clustering but real data’s patterns are likely to be more complex:

This is a much more complicated network! Parsing biological meaning out of this would require more work than the first example with 5 very different distributions, but there is a pretty strong cluster in the upper right corner of plants with low fertilizer at the end of the experiment. In general if you pick to use EMD with or without networks start small and consider what each step should mean conceptually for your experiment.